Do i have the wrong transmission

I would check the tires first, they can cause a vibration at a specific speed when one goes bad (like a broken steel belt internal to the tire). Do that before spending the big bucks on a transmission diagnostic. Any decent shop should have a tire balance machine.

What fixes have you tried??? Kenf is correct, start at the tires that's the simplest n most likely. The 727 model is an older model of Chrysler tranny. The 2000 model Dodge 1500 4x4 used (I believe) a 46RE. The 5.9 is a newfangled way of designating the 360 CID and it's "essentially" the same bolt on block as when it was introduced. Therefore, you can bolt a 727 to a 5.9 physically, minus maybe a different flexplate and adapting the tranny case to fit the crank sensor. That said, you need to narrow down where the vibration is coming from...front, back, left or right side. With 4x4 in the moniker, unfortunately your problems are that more numerous. So jack her up, all 4 wheels if possible, put her in gear n run her up to speed while your underneath n look n listen close. Even if you have open diff's, you can still get 2 wheels aturnin' at the same time.

Ive tried everything from ball joints to resetting the adnustments on my bands. It only does it at 40mph -50mph with 45mph being the worst and its only when I hold the gas pedal at a cruise pressure like if I take my foot off the pedal or gas it real hard it doesnt shake also when it starts to shake my rpms drop to 1500 evrytime

If you have RPM loss associated with the shaking n it's not because from any input change on your part, then it sounds like an engine problem. Is there a check engine lite on? At this point, you need to hook up an engine scanner that can read live data, take your electro/mechanical marvel for a drive while keeping an eye on the scanner. When the problem occurs, what are your fuel trims n O2 sensor readings.