surging confused

I have a 1999 Lumina and when you get to interstate speed and the car is warmed up it will hesitate when you push on the gas. Does it worse when on incline. I have done this to it plugs,fuel filter,tran. filter & fluid, air filter and also had put on computer no codes came up. The car dont do this until it is warmed up,idles fine.

Possible causes:

- engine running hot (at a temperature higher than normal)
- fuel pressure regulator operating at a low pressure
- wrong timing
- faulty ECM
- EGR stuck open (SES light)
- dirty fuel injectors
- vacuum leak (probably at the intake manifolder)
- worn driveaxles
- faulty torque converter
- clogged fuel filter
- faulty ignition system

It could be any of these, even if some of the causes described here seem to have no logic (believe me, they have). Check the coolant level and also add some fuel injector cleaner in the tank. Check for vacuum leaks (spray some starting fluid on the top engine, around the intake manifolder's gaskets and if that results in higher rpms, that's the cause). Is the SES light on? If yes, check the computer for error codes.

thanks i will try these causes and let you know what i find out

My 97 did that I took it to gm dealer they scanned it while driving and it was the electric solenoids in tranny.

I scanned my 1999 using a Tech2 and found the same; a Torque Converter Clutch Lockup solenoid in the transmission isn't working right. I'm willing to bet that or the fuel pressure regulator.

The only way to determine if it's the TCC solenoid or not is to disconnect it from the tranny (there's a plug on the right side of the transmission, you can see it from the top). If yhe car stops acting funny, you found the problem. If not, plug it back in and keep looking for other possible cause.