i have a 94 bronco 5.8l 4x4 manual hubs rebuilt motor tranny front and rear end. I have been having this vibration problem ever since i had the drive shaft replaced. i thought i was hearing a grinding noise but after getting more opinions and listening more closely its definetly a vibration. this loud vibration only happens between 20 and 30mph if i'm driving nicely but if i drive the truck like i stole it everything is fine. if i let off the gas while this is happening it will stop or if i stomp on it i will get no response until it downshifts making the vibration stop.???????? is my driveshaft just out of balance?