Well dont know what it can be, and dont really know where to start? 2001 sunfire 2.2 auto 76,000 new wires and plugs. All fluids look fine and proper levels.
Now im averging around 22 -25mpg maybe. Get around 280 miles from the full mark to the quarter mark. Now the issue, it fells like it has a slight miss or loss of power.
When ideling its at the 600 rpm range. Now driving down the road if im cruising say at 45mph and give it some slight peddle i can feel the power going in and out. At that point it is not a consistant up and down in power, more like a in and out feel like something is trying to work or something. Also it just seems i have to give it more than half peddle to get anywhere. To me it fells like the stall converter trying to lock up or something. Also noticed at 3rd gear when it shifts to 3rd it kinda does a high rev then goes in.

I dont know if its the tranny but to me it seems something is wrong and not sure to start. A buddy of mine has a shop and has a tranny flush machine and i think ill have that done to start off to see if that eleminates that. Any ideas anyone?? Think its the tranny messin with me?

At any sign of a loss of power, the first things I would change are the fuel and air filters. I've seen this clear up many problems which initially seemed much more serious. Proper fuel pressure is essential for any newer vehicle to run properly. Even air filters can look "okay", but actually may be significantly restrictive due to fine dust. If it hasn't been done before, definitely start with the fuel filter. I know it's a pain to get at, but it was the culprit in both my car and my brother's. I've always found it strange that GM never put a maintenance interval there for it. I've seen other manufacturers here typically require changes between 25,000 and 50,000km (that's about 15,000 and 30,000 miles). I wouldn't dig any deeper until you KNOW that these are in good shape. I once got a tank of gas in Lewiston NY that had my filter clogged solid by the time I was just under 1/2 tank, so even if it was changed a year ago, I would do it again. The symptoms you describe could easily be attributed to this - and it's a cheap way to start. When I worked at a GM dealer about 15 years ago, those filters were a standard part of any tune-up we did.
John

Funny, mine just started almost the same thing yesterday, like merry christmas, you are about to spend more than you wanted to this year. I was driving back to work from lunch and just cruising on back streets once up to 30mph the car just seemed to stall but then would rev high before seming to shift. All fluids are where the should, 75k miles. Did notice however that the sensor on the header was smoking?!?! Luckily I live less than 1 mile from work. Car is 2001 base model 3spd auto. I will have to do the same and take down to shop.

actually on mine, it is in 2nd gear and doesnt want to go to 3rd. It did throw a code 4 days ago 0125 but have not looked it up yet

I thought at around 45 mph is when the converter does lock up. On my Cavalier I try to either drive over 45 or under. If you drive at 45 the tranny does not know whether to lock up or not.