1998 Pontiac Grand Prix Engine Stutter/Hiccup

I have a 98 Grand Prix 3.1L V6 w/ 143,700 mi.

For the past 3 weeks I've noticed that while driving between 45-55 mph, my entire car would jerk about 4 or 5 times real quick and then stop. It wasn't just the steering wheel or wheels, but the entire car would stutter and then work fine. (It almost felt like going very slowly uphill in an ATV and having the wheels slip and catch several times in about 2 seconds time). This would happen about twice a week and only once a day.

In the past week, it has increased in occurence and become a little more harsh. It now does it between 40 and 60 mph (once at 30 mph going uphill) and I've noticed that when I press on the accelerator while it does it, the car wont respond and the RPMs stay around 1500-1800 (this is where my RPMs run at 55mph). If press down a lot on the accelerator, the stuttering stops and the car accelerates nicely. It also stops stuttering if I take my foot off the gas completely.

Never any major engine trouble. Recently had water pump and fuel filter replaced.

Taking it to a mechanic on Monday.