Truck Stutters While Driving - Need Help Diagnosing Problem

[Extremesolo]

My truck will stutter while I am driving it down the road. The feeling is almost "jerky" and it only seems to do it between 35-50 mph and below 2K RPM while I am just chugging down the road. I do not see any effect on the RPM gauge while it is doing it. It almost feels like there is a trailer behind the vehicle tugging on it when it acts up. Outside temperature does not seem to effect it as it does it in the summer as well as now in the cooler fall temps. I do not notice it at highway speeds and don't notice it while accelerating. I am not saying it definately doesn't do it then, just if it does it is not very noticable. I have had the CPS recall done about a year or so ago. I also thought it may be a throttle position sensor issue so I went to the bone yard and replaced my factory fuel pedal with another one and it has the exact same issue. Please chime in with any other suggestions as this is very annoying and I would like to get it fixed. Thanks.