First off, I live near Green Bay, WI and this winter has been BRUTAL! Seems like every day has been at or below zero since December! Probably part of the issue. Now onto the issue at hand:

I noticed a couple days ago that it was running with a fluctuating idle at red lights on my way to work in the morning. RPMs at or slightly above 5k but well below 10k. I turned off my heater and the idling problem seemed to go away. Okay... engine running better, but I'm freezing my ass off... oh well, I'll deal with it.

Tonight after work I had some errands to run across town. Well, the idling issue got so bad that it almost died a couple of times. At red lights, I would have to throw it in neutral and press on the gas just to keep her running. When driving, it would lose power and pressing down further on the gas wouldn't do anything. Stopped and filled up (little over 1/4 tank) at a different (known good) gas station (Kwik Trip) and got a bottle of injector cleaner right away.

Went onto my errands and problem still there. Turned around and went home and engine seemed to be running slightly better. Could it be bad gas from a different gas station (Express)?? Both have no ethanol added to their premium and (I believe 91 Octane).

Also... replaced my fuel filter and HP line in October. Any help would be appreciated. If you made it through my "novel," thanks!

You should start by checking your ETA and wiring harness. From there check fuel pumps. It sounds like one or the other.

I've been wanting to check out the wiring harness for a while now with all the things I've been seeing on here about them. Finding the time to do so has been a bit of a challenge though. I'll see how she behaves this week with a full tank from a different gas station first. If this issue seems to get better, I'm still going to check the harness once it gets warmer. Along with welding up my Jerry-rigged exhaust from a couple months back (have a post on that too).

I've had this car for a little over 3 years and it's been nothing but gremlin after gremlin. If I keep this up, the cash I stuck into this car would be enough to buy a brand new E-Class (bit of an exaggeration, but you know what I mean)! Thank you for the advice!

An easy check is to pop the hood and check the two plugs on the top of the water pump. You'll be able to tell by the color of the wires (pic below). Takes all of two minutes. If you don't see a bright blue wire on one of them then you've got a old harness.

check the wires in the throttle body harness too.

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Even though it's only Wednesday, I haven't had the same issue all week with a different company's Premium from last Friday. At this point, I'm almost certain that it was bad gas. Guess I won't be filling up at an Express Convenience Center anymore...

So here it is, about a month later and I'm having the same issue. I only live about 5 miles from work, so I only have to fill up about once a month (which is excellent!). I noticed today that my fuel gage is slightly above 1/4 tank - pretty much the same level as last time.

So, I'm pretty sure I have some crap in my gas tank... anything that I could do to clean this out without dropping the tank? That would most likely be a pain in the ass.

Getting the tank out actually isn't very difficult so long as it is empty.

You should try to fill it up first and see if the problem goes away.

Filled her up last night and she runs like a dream now. I received a couple PMs from someone to check the OVP and most likely replace that. I'm pretty sure that it's an old one and it will have to replaced. $18 on Rock Auto, so I'll order one up and hope that fixes it

Collin is most likely correct. I had almost the exact same issues that you had but I knew the main wire harness was good (I replaced in just 2 years earlier). It ended out being both fuel pumps when bad. On the bench when I tested out the fuel pumps they only worked maybe 40% of the time I applied current to them. I had to "deal" with this issue for 5 months (and two tows). I did replace the OVP and a host of other things before replacing the two expensive bosch pumps. I recall my wagon working well 1-3 weeks stints between the hiccups arose. Keep an eye on it...

Now that it's finally getting warmer in the artic known as Wisconsin, my tank is pretty much empty and I haven't had a single problem with my acceleration issues. I'm thinking the cause was from one of these issues:
1 - My car is like everyone else up her and hates the cold
2 - Still had some bad gas in the tank (from what I expected earlier) and now it's burned up
3 - Possibly had some ice buildup in the ventilation hose from the gas tank

Whatever it was, I'm glad it's gone and hopeful that it doesn't return!