Chevrolet Repair: 1994 S10 Lean Surge, throttle position sensor, fordscorpio

Question
I am chasing a lean surge in a 94 S10 4.3 (W) engine. The truck runs great while in open loop, but as soon as it goes into closed loop it has a lean surge and power loss. I have checked fuel psi (62psi), I have also replaced O2 sensor. I was having trouble with the EGR valve getting carbon stuck in in so I cleaned it out and installed a gasket with a screen in it.
Thank You!
Scotty

Answer
Throttle position sensor is possible.
So is a dirty MAF.

http://www.fordscorpio.co.uk/cleanmaf.htm
Yes, a Ford site, but they work the same.

Temp sensor is another possibility.
http://www.chevytalk.org/threads/showthreaded.php?Cat=0&Number=1366279

And check that fuel pressure going down the road, while it is surging.
Van