95 century stuttering

I have a '95 Century with the 3.1L. It stutters badly on the highway when trying to ease into the accelerator or any time a little more load is applied to the engine. If I floor it then the stumbling stops and it accelerates normally. Leaving stop lights it will also stumble but not as badly as when it is at cruising speed on the highway. Any ideas on what may be causing this?

How many miles?

Try the simple stuff first:

Check air filter, replace fuel filter if it's original, change the spark plugs if original, check for vacuum leaks, use premium gas and fuel injector cleaner for a while. After you do the simple stuff then you can do diagnostics

Ditto the above stuff and possibly a sticky TCC solenoid...

Thanks for the replies. The car has 154,000 miles on it and I just replaced the fuel filter. I will go ahead and change the plugs and run some injector cleaner this weekend. Do you think that it could have anything to do with the MAF? I'll try to clean that up and see if it has any affect.

May be the... MAF.. EGR.. or a sensor????? all of which I know very little about.

it may not be the spark plugs but I always change them every 50-60k miles, makes the car start easier