GM-GMC: 1990 GM Sierra 3500 7.4ltr, oxygen sensor, chevs

Question
Hi,

I am having some problem now for some time now. when starting my truck up from cold, it runs perfect, no hesitation, as soon as the truck starts to warm up or is at normal operating temperature during acceleration it hesitates, sometimes when it idles I see the rpm gauge go from 900 to 700 then jumps back up to 900. I have put, new plugs, wires, rotor, cap, fuel filter, and still does this, last year I put new oxygen sensor and I don't feel any restrictions in the exhaust as its blowing out hard like normal or better... Any idea's??

Answer
love the motor. works well in my 70 chevelle..... however there have been some problems with the distributor pickup coil in early 90 chevs   maybe you should try a used distributor as a test....  yours could have a cracked magnet which will cause the engine to hesitate or sputter on acceleration