I recently have been having hesitation problems with my 2002 Bonneville SSEI. When i go to accelerate (25-40% Throttle) the car will hesitate a fair amount, once the RPM'* get somewhere above 2700 the car will regain its power and take off for the most part like normal. When i scan the car with my AutoTAP scan tool i notice that the Long Trim Fuel Percent runs at about 5-10%. I tried cleaning the MAF which seemed to help a little bit. I put in one can of seafoam cleaner into the tank, and that didnt help very much (But i havent burnt the whole tank of gas yet, so that might change). My O2 sensors appear to be working correctly. And for the most part of what i can tell all of the other sensors are functioning normally. I have been having problems with the sticky Delco Pressure control solenoid in my transmission, after replacing the transmission fluid and filter that issue has largely gone away. Maybe thats part of it???? So im a bit lost now, any help would be greatly appreciated. I can provide graphs of data for troubleshooting purposes if needed.

Have you checked your Fuel pressure? Plugs/coils, vacuum lines?

Plugs and wires account for a good chunk of problems. I'm with John on checking/replacing if they are old.

Well i tried using some "STP" injector cleaner and i noticed a very large difference after about 30 miles of driving. Also now that i think about it i started experiencing these problems right after i filled up just like Joe Papworth'* Bonneville. Must have just been a bad fill up of gas. Thanks for your help guys!