when i set the cruise on my 01 the truck seem to pulsate i normaly set it between 60-70 mph i notice a 100-200 rpm movement in the tack this happens on flat roads any idea would be helpful

 

Does it control the speed (MPH) ok or is that pulsing as well? My first thought if it's factory cruise would be to look for a vacuum leak and see if the speedo reads steady without the cruise on. Speed is read from the rear wheel speed sensor with the PCM controlling vacuum to the cruise servo. If the speedo reads steady without the cruise on then you can probably rule out the speed sensor. Ensure that the cruise servo is securely mounted to its bracket,as any slop will result in "lost motion". Check to see if you have any codes for the PCM, but I doubt thats your problem. It sure sounds like a vacuum problem or cruise servo problem. The servo has a small clip that attaches the cruise cable, any wear here could give you some variations.

After market cruise surging is nearly always caused by too much slop in the cruise servo cable where it attaches to the throttle arm. Never have more than 1/8 inch clearance but you must always have some clearance. After market cruise can be set up to control RPM and not MPH.