I have installed a 2 speed gear vendors overdrive on a 2006 5.9 cummins 3500 and when the truck is loaded it seems like the clutch is slipping in 1 and 2 gears but 3 thru 6 it never slipps it will also kill the engine with brake on and letting the clutch out in 2nd gear. I wonder if there is a clutch in the 2 speed that might be slipping.

 

Sounds like you don't have all the electronics wired in right. It's supposed to be locked out until over around 20mph or so, which pretty much rules out 1st and 2nd gear on a manual.

 

The overdrive is in direct drive bellow 20mph, but I didnt know if there was a cluth that ingaged the overdrive or direct drive if one or both are looked in by a clutch I thought it might be slipping. Thanks for the reply.

 

No, direct is direct, as in splined shaft, gear-meshed direct.

I don't get the part about killing the engine in 2nd with the brake on. That sounds normal. If I wanted to stall the truck with the clutch, that's how I would do it. Maybe 3rd. Why would you do that?

 

That is why I am having trouble beliving it is the drive clutch. It will stall the engine just like it should but when you start to drive off with a load it fills like it slips in 1st and 2nd gear but then doesn't do any thing wrong in the other gears. If you try to stall it it will not slip.

 

Then my guess would be it is slipping the clutch in front of your G56.

 

I believe we fixed the truck what felt like a clutch sliping turned out to be the swing bearing allowing the drive shaft to chater.

 

That makes more sense now.