I have a 2001 Pontiac Firebird 3.8 Auto with about 107,000 miles on it. My problem is when I am on the road, and when car begins to down shift from 4th to 3rd gear at about 3/4 throttle, car begins to hesitate at about 3500 RPM. I have since replaced all plugs, wires and coils and problem has improved, but is still their. Car will accelerate at full throttle no problem. I can get the car to hesitate almost exactlly at 3500 RPM and at 3/4 throttle. Full throttle and hesitation gone.Car also runs perfect otherwise. I cannot get any codes to trip on car either. Any thoughts? Gas milage has not been effected either. I get consistant 23 MPG Av. From a dead stop, car will go threw all the gears just fine and rap out at about 5500 RPM in first and second. Wonder if it is a MAF sensor problem, or some type of TPS sensor problem. Car acts like an older car with a vacume advance problem or like secondary butterflys on an old 4 bar. carb wont open. Any help???????

on the main page, scroll down to tech info, test procedures, theres tests for tps and maf