700R4 problem

[85 K5]

85 Blazer, 350 and 700R4. 45,000 miles on 700R4 rebuild

Problem is while trying to cruise at 40-45 mph it keeps shifting between 3 and 4. Bouncing back and forth, shifts maybe twice per second. All other shifts are ok. Accelerating through this speed range all acts ok. 50 mph and above it stays in 4th and converter locked up. Got a good hard 1-2 shift. 40-45 mph is the only time it does this and that's the only problem there is.
Trans fluid is red, does not smell burnt. Also it's not the lock up converter shifting in and out, if it were it would do it at other speeds above 50 mph. Is this the servo or the governor gear? TV cable is adjusted properly.

Thanks in advance for your suggestions.