acting weird

hey everyone. gotta quick question about my friends new-to-him rodeo. its either a 98 or 99. i dont know much abotu it, but this is a pretty generic question. whenever he lets off the gas to slow down the rear end start shaking almost wanting to fishtail. thanx for any help
-daniel

could be low on gear oil in the rear, or the last person to change it didn't use the gear oil with the LSD additive.

e-brake hanging up?

Yeah, something is braking the rear definitely. Do you hear any skidding sound?