transmission overdrive on 1995 Dodge Ram 3500

If I select drive when moving out on the highway the transmission kicks in & out steadily when it gets to the speed overdrive kicks in. The overdrive doesn't lock in --- it just continues to shift in & out constantly. This is a rebuilt transmission with 20 miles on it. I have run it only to test it in high. The rest of the time I have kept it in the next lower gear so as to not damage the trn.

1 answer
Go back where you had the job done. Hopefully you didn't do the job. If so I would be calling the company where you bought the tranny NOW!