drive train problem

[mumbles84]

i noticed a vibration in my truck for a while at 2 speeds 35 and 60 i change all the u joints still has it. latey i noticed when back up in to a parking spot the right rear tire hangs up then when i go to drive away it needs more acceleration than normal. dose not do it when i back out of my drive the fluid in the rear diff neads to be changed it has water or lot of metal in its grey looked like water to me. im thinking spider gears?

 

[HolyRamBatman]

Is the fluid low? Changing the fluid is a cheap and easy place to start. Drain the fluid and pull the cover and let the inspection begin.