I would have to see exactly what is going on to say whether this is normal or not. Engine RPM and speed are directly related....let's say you are cruising down the freeway at 65 mph on cruise and bump up the set point to 66 mph. The engine rpm has to increase slightly for the speed to increase. 1 mph difference would be a very small difference in rpm but may be noticeable (depends on the vehicle and setup, but maybe 20-30 rpm). The other thing that may be happening is that if you increase the cruise setpoint it means the truck has to accelerate to get up to that speed and therefore may unlock the torque converter for a short period of time until it reaches that point. In this case the rpm would increase by maybe 100-200 rpm for a short time and then drop back down.
