I have an 04. 4.3 blazer. 4x4. Been a great vehicle...within past week this just started...first off no engine lights....cruising down road between 40 and 60 mph with OD selected on selector the rmp will go from 1400 to 1800 back and forth non stop...if I let off it stops....if I speed up and dont stay constant speed it stops...I've looked a few places but no real answers...I've seen people say the tcc solenoid...any input I appreciate it before I tear into it

 

It's the TCC engaging and disengaging.