Hi Folks- Its been awhile, but still having ongoing problems with bucking under throttle while warm and fishbiting at steady state at times.

Had my 99 out yesterday and under load (going up a 1600ft grade- Little hills in Oregon on the Coast range) at 55-60, the engine surged and bucked...I took my foot out of it and maintained the hill at a slower speed, but it definitely felt starved of fuel.

As I got to the end of my trip, a few times accelerating from a stop and performance was way down.

I am getting boost on the hills ( upwards to 7psi or so). I ran yesterday without my Kennedy boost fooler as I hadnt put back on and recalibrated yet after the IP was replaced.

Recent history- Last fall had the IP replaced, the optical sense ring had broken. Tech timed and set base timing. Starts and runs great, maybe a bit more smoke on startup than before, but it sits a lot.

Lift pump is a new GM. It is putting out barely 3psi with the engine off. Doesnt move the needle when the truck it idling.
Flow is good from the lift pump with engine off and engine doesnt sputter or die when I open the bleed handle while its running.

Engine Fuel filter is new.
Fuel is clean and new, tank was 3/4 to full at the time.
No sock in the tank.
When opening the fuel cap, I hear a "whoosh" - dont really know if it is pressure or vacuum.

Have experienced the problem prior to even replacing the IP.

Having been around in circles on this for the last several years, it just seems like it just doesnt get enough fuel for when there is a demand.

I did notice last night that it doesnt appear to have the Optical encoder Filter on it, which I thought was standard for the 99. But in any case, that might explain the fishbiting, but i dont think the load performance would be the case.

I am really leaning towards a higher volume, higher pressure lift pump as I am at a loss to explain the power loss issue.

It definitely did this after driving for the first 75 miles yesterday and getting it warm...I am going to try to take the fuel cap loose and repeat, thinking maybe the tank is getting a vacuum and not being pressurized....

Any thoughts?