1988 k2500 goes into "limp mode" when accelerating going uphill

[TheKOOK]

On my ( since sold) '88 C2500, 5.7, My fuel pump started to fail... it was intermittent at first.
( you mention, " as you are driving uphill" )..... I remember, when the pump was going bad, .. And the symptom was happening, The less I had my foot on the gas, the better it ran. When I went a tad faster, my truck had the issue like a 'limp mode'....
Changing the fuel pump was the fix.

On Saturday after work I swapped out the fuel tank and fuel pump as the tank was most likely original and was coated on the inside with some sort of gunk that looked like salt when it dried out. I didn't mention this before but I recently went on a decent road trip in the truck, which is when the no power uphill issue started for me. once i got the truck back home I disconnected the fuel line after the filter and the gas looked like lemonade. It was extremely cloudy and contaminated which is why I decided to swap out the tank and pump. Anyway I've been driving it a lot since Saturday and so far the truck is driving very well. I'm no longer loosing power going uphill and it feels more responsive. So I believe I had the exact same issue as you and the new pump and tank fixed that issue.

 

[TheKOOK]

Incase anyone was curious I didn't get a chance to look at the wiring for the ECM (neighbors don't want me doing any kind of repair work in the drive way...). So far the truck starts, idles and is running very well with no SES lights coming on since Saturday. Is it possible the bad fuel pump was causing the ECM to freak out? I'm guessing the lean code 44 I was getting had to do with the fuel pump not delivering enough fuel? Will the truck still run the way its been running even though code 51 is still present or is the code 51 a false positive? Should I disconnect the battery and see if the code clears and comes back? I have so many questions about this issue.

I'm going to try to look at the wiring tomorrow

 

[dhworkin]

Disconnect the battery (negative) for 15 to 20 seconds (reconnect) then check for codes.
I would check the spring in the fuel regulator if you haven’t done that. I’ve seen them rusted in half and the truck still running but not running as good as it should.