Newb here, so any help would be greatly appreciated.

We have a 2008 4x4 Trans Diesel that has been great up until now.
While driving, any time you release your foot off of the accelerator pedal it will decel to the point of almost locking the rear wheels up and will basically use the unit as an engine brake. The slower you go the less noticable it is but regardless of your speed it is fairly violent, literally like downshifting a manual transmission car at 50mph and dropping it from 3rd gear to first and dumping the clutch. The Mule will do this in high/low and is something that is new. If anyone has any pointers please throw them my way.

Not that it matters but I have a lift kit and SS rims and larger tires on the unit. Only other mods are an amp and speakers.

 

We also have a 08 Diesel 3010, and we are having the same issue. The engine brake will brake so severely that it snapped our belt. We are having trouble finding out what is causing it to do this, and our mechanic is at a loss, as well. Tips would be greatly appreciated.

 

It was the driven pulley bushing. It is a copper bushing that needed to be replaced. It was a bear to repair but it works fine now. We replaced the plastic dogs on either the drive or driven pulley too.
You have to remove the drive pulley and the driven pulley then disassemble the driven pulley to get to the bushing. It takes a special tool and I had a buddy at a local kawi shop help me with that part because it is spring loaded and has to be turned to a certain tension when you put it all back together. If you need the service manual that covers this PM me with your email and I will send it to you.