M50D only has 4th

[gribly]

My transmission was causing my truck to shudder at 15mph - I changed fluid from cooked gear oil to Mercon V and low speed vibration went away. Now 3000 miles later it is vibrating in all gears except 4th. 1st is okay, 2nd is alright, 3rd is bad, 4th is fine, and 5th is terrible. I can coast in 3rd and 5th and use light throttle, but anything over 1/4 throttle or so and my whole truck vibrates.

The bearings are probably completely shot, aren't they?

 

[schmoo]

that's more than bearings.
input qear and probably the front gear on the countershaft.