Camry :: 2005 SE V6 Engine Stumble On Hard Acceleration

I just bought an 05' SE V6, with the 3.3 engine. Seemed to run good, had it checked by shop and they said it was a good buy, so i bought it. First day I owned it, took it to toyota dealership and had them do a 90, 000 mi service. did a timing belt, water pump, tranny flush, oil change. I got the car back, and it ran like crap! It would stumble on hard acceleration, and seem to even surge a bit at times. I took it right back? Service rep tried to say I put in diesel or bad gas. I only filled up with chevron premium, which is only gas i ever use. I know how to put gas in my tank!

Any how, they checked timing belt and said it was right, but the timing gear needed to be changed because one tooth looked rounded off. That didn't work either, still stumbled on acceleration, but idled perfect @ 675 rpms. So now the serv. manager gets involved, says he wants me satisfied. they then drained all my gas, then re-fill it. then flushed out all injectors. then put in all new plugs and PCV valve. I did a pressure test of fuel system, said it was good. While they were changing the plugs, they did a complete 6 cylinder compression test and scope analysis, and it came back good, too! I pick it up cause i got to go back. It ran a lot better but still stumbles on hard acceleration on highway. drove 1250 miles back, didn't use a drop of oil.

I did notice when I got 100 miles the temp gauge dropped all the way down to second mark on cold for a little bit, but went back to normal temp and stayed there through the last 1100 miles(that scared me, so i watched temp gauge like a hawk). And the outside temp was @ 62 degrees when the temp dropped at 1200 ft. Elevation...maybe it got stuck and is ok? My CEL has never came on through all this, and it does work, I have made sure of that.

I bought this car from original owner, and they had engine and heads just replaced in 2008 at 44,000 miles at toyota dealership under warranty fot 10,000 dollars. i verified this with that dealership 3 times with 3 different reps at that dealership. old owner said he was having problems with engine stumbling, and took it in twice and dealership said it was ok each time, not throwing any codes and sent him away saying car was ok.