1992 Dodge Dakota OverDrive

Transmission problem
1992 Dodge Dakota 6 cyl Two Wheel Drive Automatic lots miles

ok when you star getting around 50 mph and on up ito 65 it starts this jumping in and out of overdrive constantly and just jerking the truck along with this back fire in there som times, and no matter what you do you have no control over it, but once it gets up to 70 mph and on up it just stays in overdrive period but the jerky part stops, we took it to the Dodge house they kept it 3 days and could not figure it out but they charged me 500.00 for time tryin too, so then I took it to a amcoo transmisson shop they had it a week charged 1, ooo. Oo replaced the o/d button and told me to never use it, sounded odd but I had never used it anyway as I do not tow anyways, so I just dont need that button, but about a yr. Later the very same problem comes back, so I decide to see if pushing this button would help at all, guess what that dumb button dont even work, never did, the light on it didnt even try to come on, I know the old one lite up, so I guess he did something but god knows what im sure not going back to get another 1,000.00button that dont work, just to drive it another yr. There has to be someone that knows what is causeing this, please help! We have spent so much money and replaced so much stuff on that truck but nothing is working, thanks