Slight "Jerking " feeling while HWY driving

Good evening all,
I don't recall seeing anything similar here, so here goes...
2000 Century, 140,000 km, No tune up yet.
While crusing on the highway, lets say... 100 kph and up, the car feels like it is giving slight jerking motions when it tries to accelerate. It isn't hugely noticable, but it is to me since I drive it all the time, and it is such a nice riding vehicle.
I am still getting great gas milage, usually 550 - 590 Km on a full tank, so I havn't bothered to get a tune up since I bought it new.
Any ideas?
Thanks

The problem you have as been addressed here before but I will help you out. The only reason I say the problem was addressed before is because just about any trans problem on this car is related to the same repair. There is a GM bullentin out for this condition and many more caused by the same thing. Your repair is to replace the Pressure Control solenoid. After any internal trans repairs it is a must to reset the shift adapts or the trans will not shift properly.

Here is the bullentin name, number and conditions that apply.

Shudders, Flares, Erratic Shifts and Intermittent Concerns, DTC P1811 or P0748 Set (Replace Pressure Control Solenoid Valve Assembly) #00-07-30-002B - (07/19/2002)

FYI I did one repair for this today, the labor charge on this is 6.1 hours of labor plus parts. It took me less than 3 hours to do the job.

OUCH!!!
Thanks for your reply. I was hoping it was a fuel filter or clogged injector.
Taking the Explorer in next week for a complete Trans. flush, I guess the Buick will follow shortly to have it looked at.
Thanks again.

My car did the same thing. 94 3.1 Century. It felt like a very minor under light acceleration on the highway only. One of the front spark plugs had carbon tracking on it. New plugs and wires took care of the problem.

Might be a bad coil pack. A new one solved similar symptoms on my '91 Park Ave.