1990 454 tbi Help

[kellydown]

Somewhat new to the website, I have 1990 Chevy v3500 454 Tbi. My problem begin a couple months ago. Been thru a bunch of old threads but cant figure this one out. Here's how it went down....

1. Truck started hesitating and missing under throttle. Idles fine.
2. replaced Egr valve
3. ran fine for a few weeks, then it started doing the same thing.
4. replaced Map sensor
5. ran good for about a month then....see #1 & #3
6. Today I did the old paperclip trick on the OBD connection. It read code 12.
Drove it down to O'Reilly's today with it running like crap. They plugged
into and it showed no codes either
7. Now I am starting to pull out what little hair I have left.

It has dual tanks, it runs the same on either tank, so I would think that would rule out fuel pump issues. I just don't understand why I would replace something then run good for a few weeks then back to the same ole same ole.
Your help is much appreciated!