Chevrolet Repair: fuel ratio prob, throttle position sensor, smooth resistance

Question
QUESTION: I have a 96 GMC Sub K2500 5.7 that backfires and hesitates at intermediate (maintaining speed) or slighly less throttle with no DTC codes.  It runs fine at 0-20% & 60-100% TP.  If I pull the connector for the MAF, I get MAF low code (as expected) and a quick sputter from the motor, but then it runs just fine.  I tried cleaning the MAF but that did not work, then replaced the MAF and cleared the code to no avail, still the same prob.  Any sugestions?

Thanks
Jason

ANSWER: Hello Jason,
I would check the throttle position sensor for smooth resistance response.

Van

---------- FOLLOW-UP ----------

QUESTION: Replaced the TPS, no go.  Any other thoughts?  Also posted the question here http://www.chevytalk.org/fusionbb/showtopic.php?tid/160993/ with more info.  Haven't had much luck though.

thanks
Jason

Answer
Hi Jason,
I love CT.

Hi Bear,
Have you checked the fuel pressure?
That downhill part is puzzling. Almost sounds like allowing water in the bottom of the tank to get sucked up by the pump, but if that were the case, removing the MAF wouldn't correct it.

Might check the EGR valve, not so much for sticking open, but rather, to see if it is opening when it shouldn't. Topping out on the hill would make the vaccume rise just a little, and the additional vacuum might be affecting the EGR, or some other vacuum controlled device...Is there a MAP sensor on that?

Welcome to CT  

Van ....(I am Fixitfox33 on CT)