Greetings: My '85 300TD has reached the point where it may be unsafe for the highway due to lack of power. This is especially noticeable going up hills, where I actually lose speed even with the pedal pegged. I don't know exactly where to start on troubleshooting, so hoping I can get some input from the forum here.

Here are the symptoms:
very sluggish off the line
harsh and elongated shifts with the (new) a/c compressor running. Shifts smoother w/o air con on
difficult to maintain speed above 60 mph
will not downshift when flooring it from speeds over 40 mph

Here are some other facts that may/may not be related to the problem:
> new alternator
> new a/c compressor, dryer, expansion valve. The center vents do not blow after a/c job, but I cannot see anything disconnected in dash
> in-line fuel filter replaced last year
> spin-on fuel filter replaced 1 yr ago
> fuel usually purchased from same place for last 7 yrs
> not much smoke from exhaust
> I believe turbo has not worked in awhile. I hear no spooling whine, but impeller spins by hand and there is plenty of suction from front intake
> air filter replaced 3 months ago
> door lock has vacuum issue and that line has been disconnected + plugged for some time
> valves adjusted last year (by me). Might I need to re-do/check that again?
> banjo bolt is clean

So, maybe I should start with the turbo? Which lines to I test for vacuum? I am looking for like 10 lb of vac? Assume that I need to drive the car w/vac gauge connected to test this?

I am open to all other troubleshooting suggestions.

Thank you in advance for the help.