99 lhs 3.5

I have noticed that just recently at about 55 mph the trans. Feels like it shifting from 3 to od and back. Below this speed and above this speed it feels normal
Fluid levels are good. Also noted that the cruise will turn on but not engage.
Any ideas?

Also noted after last tune up, oil light flickers at idle, if the old Chevys did that it was usually the cam bearing, what about Chrysler ?