I am getting a weird vibration once I let off the gas pedal from the speeds of 55 and above once below 55 it goes away. If you even put the slightest pressure on the pedal the vibration goes away again. The truck is new to me with 50k miles on it it had a rear seal that was bad on the transmission they replaced the race and bearing as they are pitted but the vibration is there

 

Help please