Scenario; Traveling on interstate highway empty, without trailer, at or below posted speed limit with cruise control w/o tow-haul engaged, and crest small hill and begin long descent. Truck immediately begins to downshift and slow truck. Within ¼ mile truck has decelerated to 60 mph from near 80, and engine is taching somewhere near 4500 rpm. I was able to regain control by shutting off cruise and manually controlling speed. This happened once before, on a different grade, a similar scenario played out. Except, I had one heck of a time resuming speed. I was unsure, at that time what I may have done to contribute to the issue since on long descents like this, with curves, I will sometimes use manual mode to downshift into a lower gear to control speed. Yesterday’s incident, truck was in drive, with cruise, and starting descent of 5+% grade. I usually don’t do anything on this hill for the first several miles because road is straight w/80 speed limit.
Any suggestions or thoughts would be appreciated. My thought (guess) may be a program glitch in the tranny control module?