Rpm's keep on rising and falling while I drive
2 Answers
does the truck do it when you're accelerating hard? if so it could be the transmission slipping.
I'm guessing it needs more power at times when going up a hill so it down shifts to do it. 55 is a low speed with cruise on, down hill or flat ground it will probably be fine in 4th gear with the torque converter locked. If you start going up a grade it will unlock the torque converter and may even downshift to 3rd to maintain 55.