I'd recommend getting the evap. valve replaced, even if it doesn't directly relate to your current issue. Ask them (the dealer) if it falls under any emission warranty. I think taking a fuel sample and checking for water is a good idea. How many miles are on your truck?
That rules out worn spark plugs. I suspect fuel starvation as the problem. You could have a restricted fuel filter, a fuel pressure issue (too low), or something going on with the throttle body. If you live in a climate where there is lots of rain/moisture I'd start with a fuel filter and see what happens. Also your evap. problem may have something to do with this so I'll re-recommend having that repaired.
have you checked the mass air flow sensor this is located between the air filter (breather) hose running up towards the throttle body. try cleaning it out parts store sells a product just for that
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I don't think it would be your MAF if it is only when you press the throttle. I would say check your throttle position sensor because that sounds like it may be your problem. If not that then I would say a fuel problem, probably a blocked filter. Hope this helps you solve your problem.
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Poor fuel or water in the gasAir leak/vacuum leakFaulty throttle bodyAny warning lights coming on?
engine light is on but that is due to a bad evap valve,gm dealer drives it and can not find anything
27000 miles
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