Help Needed Please!!!

Hi, I have a 2001 Buick Century that has now reached 106534 miles, I bought the vehicle pre-owned but it was in great shape mechanically and esthetically and only had 50K miles. Recently I've noticed that as I accelerate the vehicle there are some sudden "shudders" or "jolt" coming from the engine compartment, the engine works fine and the check engine light has never been on. The sudden jolt only happens when the vehicle exceeds ~40 MPH and happens mostly during acceleration, seldom happens when the vehicle is cruising. I've done regular maintenance on the vehicle so far, the only things I’ve not changed so far are the transmission fluid as I was recommended not to do so and the spark plug cables. Other than this puzzling problem the vehicle works fantastic.

Welcome to AF!!

Change the fluid and filter in the transmission, just don't allow them to flush the transmission as this can damage it. A fluid and filter change will not hurt anything. I think your entire problem may be due to a dirty filter in the transmission. When you ask the transmission to shift it is having issues. When you change the fluid and filter add a can of Sea Foam transmission additive or a bottle of Lube Gard. This will free things up and may eliminate the issue. If not have the trans scanned with a trans capable scanner which will tell you if there are any internal issues with the transmission.

As for the spark plug wires, change them. Since you no CEL I doubt they are causing a problem but with 104K miles it is time to change them anyway.