Sounds like 2, 3, 4 to me although you may be getting a stacked shift so it could be 1 and then a jump immediately thru 2 to 3 and then 4. You should be getting three shifts after starting if you are starting in 1st and not stacking shifts.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Could this whole shifting issue be caused by things being improperly plumbed?

Could be vac problems.

I'm not aware that vacuum problems can cause a failure to go into first gear.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Some other updates:
The kickdown switch under pedal seems to do nothing helpful in my case, as far as i can tell. When starting from stop, it does appear to start off the car in the same gear as putting it in L, which i do believe is 2nd until this problem is fixed.
I'm optimistic about this vehicle's power in the not too distant future, as it really runs nicely once you are up above a certain range. I also am thinking the turbo re install was a good thing in the long run.
I feel like something is off and inhibiting the vehicle from ever being in 1st. It's the theory that makes the most sense. The power seems healthy when running at gears that are appropriate for the scenario. It just seems like that matchup isn't happening until i get it going fast.
Does transmission fluid maybe have anything to do with this? I haven't done a check on that yet.

Wondering if vac or trans modulator adjustment could address possible stacking problems?

300Drestoration,

As BillGrissom stated, the end of the vent line (circled in yellow) should be uncapped and re-routed into the cabin through the grommet on the firewall (red circle).

You can add a small clear inline filter (lawn mower fuel filter) to the vent line. Many places sell them. https://www.grainger.com/product/4EPA6&AL!2966!3!166588183198!!!g!82496520597!?gclid=CPKu9oS_0tMCFQNqfgodDcQGbQ&s_kwcid=AL!2966!3!166588183198!!!g!82496520597!&ef_id=WJIwMwAAADElghuV:20170503004307:s

This will correct a plumbing problem that is present.

Attached Thumbnails

 

__________________
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

At post #17, picture #2, just below the "Y" connection close to fender well. Is the clear looking filter, there should be a hose to inside cabin, but I don't think that's your problem.

What is that? And what connection point of it would go to cabin?

Also, with these open lines going to cabin, how far inside the grommet entrance do they need to go? Do i need to extend the lines so that they reach in a foot or so?

Attached is link to "Functional diagram of vacuum line routing" for model year 1985 cars with engine 617.95 to help you sort out your vacuum line routing.

http://peterschmidtransmission.com/mb_files/vacuum_schematics_77-85.asp

The VCV (vacuum control valve - item 65 in the last two diagrams) does need a vent line to the passenger cabin (item "a" in the last two diagrams) to function as intended.

The vent line is the one circled in yellow in the thumbnail (modified from your second photo in post # 17), it is also the one you are holding in the photo in your post # 9.

A small fuel filter on that line will prevent contaminants from the cabin from entering your vacuum lines.
Similarly, a small fuel filter on the brown vacuum line to the SOV (shut off valve) on the back of the IP (injection pump) will warn you of a failed SOV diaphragm by showing the black engine oil (from the IP) on the paper element of the filter.

You actually do have a lawn mower fuel filter being used as an air filter in your present vacuum line setup (as shown in the white circle in the attached thumbnail).
It is hard to tell from the limited view, but I believe it is part of the EGR circuit and was added in as a early warning indicator to show soot from a failed EGR valve.

Keep at it and you'll eventually get everything sorted out.
By the way, have you done a valve adjustment yet?

Attached Thumbnails

 

__________________
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Also, from looking at one of your earlier pictures, on an unrelated note but possibly related to your acceleration problems:
Looks like your primer pump was all wet and leaking, it is the old white style which is known to leak(and also let air into the fuel system) if you replace it with the newer style black capped version, it may help you out.

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97 e300d, 78 300Dt, 95 E300d, 94 E320 estate

Amazing. I would like to pick up some filters locally so i can do this today, and there is a home depot nearby.. How about these? Power Care Universal Fuel Filter-H-FF-125A - The Home Depot

I will add one of these filters to the currently mis-plumped and loose line and then feed the end of that into the cabin. How deeply into the hole should i send the line?

What happens if the EGR valve is failing? I i have attached a close shot of that clear colored filter that had been added to show soot buildup. What do you think of it's appearance?

No i have not done a valve adjustment but a local mechanic told me way back that when i had the vehicle in better shape that he suggested he do a valve adjustment. Is this something i can do myself? The more i can do, the better. I'd like to keep maintaining on my own as much as i can.

Thanks, yes i had been aware of that since i did in fact change both fuel fiiters myself as the first step in all of this. Thus i had to prime it and go through the pleasure of pumping fuel onto the ground via this primer. it's a common problem and in the end i vaguely remember concluding that i should change that out but it might not do anything in regards to acceleration. At this point i am feeling like the issue is more about shifting. I might take it on the highway and give it a push to see if i find a gear "D" if we can call it that. I've only found A B and C.

Just took a quick look at some plumbing.. Here's something concerning..
At that spot where my loose line should be fed to the cabin, according to the diagram there should be a split at that point, which then leads to another Y split. The initial split doesn't seem to exist in my vehicle.

More updates, while on the road..
The turbo definitely works!! Hooked up the boost pressure gauge and I'm definitely seeing action. I believe I remember reading that the pressure should hit 10psi at 4000 rpms. In various instances I have seen the needle bouncing in the 8 to 10 range and I'm sure I could have cranked it harder but wanted to exercise caution still.
I will be picking up a few fuel filters from Home Depot..
I also inserted the loose (and uncapped) tube into the hole into cabin. Indeed there was one hole available in that multi hole grommet junction, so it's probably safe to say it yet popped out and someone didn't know what to do with it.
However my concern is still regarding that connection point on tha tube. As stated above, it appears that a whole section of plumbing is missing. And it doesn't appear to be related to the non existent boost overprotection section which is also missing/removed. Or does it?