GMC Repair: Savana 2002 vortec 5700 v8 sfi engine problems, fuel injection system, sticky valves

Question
I bought this truck new and started having issues in the first year. The dealer claimed they could not replicate the problem. The service engine light would come on when I was speeding up to get on a highway or going up a steep hill. The light would come on as it slipped into the last gear and the truck would shutter and loose power and act like it was going to stall. No backfiring just loss of power. I brought it to a non dealership mechanic after it was out of warranty and he pulled multiple trouble codes for mis fires on random cylinders. These were the only codes recorded so I guess the dealership forgot to tell me this. My Mechanic did a complete tune up and then replaced the fuel injection system(spider) with a new one(new style). It seamed to solve the problem for a while but now it is even worse than before. What could the problem be?

Answer
Hi
I would guess it is an oxygen sensor.
ESPECIALLY if the misfires are all on one side (even or odd cylinders). If this is the case I would almost be certian it would be the front oxygen sensor.
A faulty cataltic converter will also develope the same symptoms you have. If it is the Cat, it has an 8yr, 80,000 mile warranty from dealership.
If it is not solved by these, it very well may be you have a mechanical problem, cam lobe(s) or sticky valves.
I Hope this helps.
Please follow post back if needed.
Good Luck
Pawl