Like jd110 said, check you load match button to see if it is on. Your speed will vary depending on terrain and load if load match is on. With it on, it will sacrifice speed in order to maintain rpm and then it will speed up with less work on the engine. I leave mine off most of the time because I can't stand the changing speed. For me, it is really only used for FEL work and even then I usually leave it off. It is more automatic for me to vary the hydrostat with my foot rather than have some computer do it for me.