Alright I've finally come across a problem that "search" hasn't been able to answer for me (first post woohoo!) Ok here's the deal:

So I wake up one -40degree day (problem's cause?) in WI and start up to go to work...A/F gauge is blank for the first time ever. Idle is fine, but it runs a little shaky at lower speeds (sometimes power cuts, sometimes stutters a bit, no real big noise indicators). Drive for a day or two like that and realize my tank is empty when it should be at half! I've been filling up with small amounts since and I'm getting between 8-10mpg. Hella rich. I've needed a new o2 sensor (says an old CEL) so I get that and slap it in. No change. Next day I switch the plugs out. Carboned up like crazy, as assumed, but still no fix. I reset my ECU and wait to see if I get CEL, sure enough I did. Tricky part is, it's giving me the lean bank 1 code. So it's gotta be some sensor tripping out saying lean and dumping fuel in, right? Problem is finding the bugger. It's not my coolant temp sensor, unplugged that while running and it almost died, and it's not my charge air temp sensor (bought a new one and put that in, no change). I've "stethoscoped" my injectors and they all sound to be running at equal rates, and not too loud. My K&N intake is also breathing fine, and my MAP sensor filter is in place.
In addition when I put it under boost (<5lb) or WOT, the A/F gauge lights up like it's being zapped with Christmas cheer.

Specs:
T-25
Vortech FMU
Walbro 255lph HP fuel pump (in tank)
(w/ stock injectors)
custom straight pipes

Any ideas? You guys rock, and any help would be appreciated!

EDIT:

What kind of o2 sensor did you get? And what year is your car? You are using the missing link? If so, remove it and see run just the MAP sensor and see if it's any different. What was the exact CEL code it pulled up?

Year is a 97.
I got the 4 pin OEM o2 ($$), can't recall the brand but it was nice and shiny ;)
Yes it has a missing link. That's what I meant by MAP sensor, but I put that guy on so long ago I had forgotten what it's called! Thanks for the quick response, any ideas?

Oh, and not 100% on the code, I believe it's P0171 (lean bank 1). I can try pulling the missing link after work, however it looked pretty clean/functional from what I could tell when I inspected it yesterday. Thanks again!

Missing links are known for having problems. If it turns out to be the culprit, get an FCD. Actually, get an FCD either way.

So I found out my new front O2 sensor I bought was dead out of the box. Awesome. Don't buy from oxygengeek.com. Went and got the OEM replacement ($90) from Checker. Works better now but needs to warm up for quite some time and doesn't cycle. I believe it's from my backside also going to crap on me. I'll keep the post updated.

As a counter point, I purchased both of my replacement O2 sensors from oxygengeek and have had no problems. :shrug Sometimes items are defective.