Bucking at constant speed? Options

[6GenCircleLghts]

After I've been driving for 10 minutes or so and I'm going down the road in 4th at 35mph with my foot barely on the gas pedal. I don't get massive bucking but enough that it annoys the hell out of me. It also happens when I'm in 3rd going 25mph and 5th going 45 to 50mph. Two main things that were replaced were the timing belt and distributor. Though I got the distributor replaced a couple months after the timing belt and that is when it started happening. Would it be from the distributor or what? The timing belt and distributor was done by a professional mechanic. I did the starter by myself, plugs and wires, but these were even before the timing belt/distributor.

[Nartanian]

The bolt holding the distributor might be too loose. I had the same issues after a head swap. The car keep bucking when you slightly tap the gas pedal. As I was driving one day, the distributor just popped out. So make sure the bolt keeping the distributor attached it tight.