There are two manuals available for it, 5 speed and 6 speed.

The combo I found is pretty rare and was a custom order. Duramax, 6 speed 4x4 3/4 ton, crew cab. You can't get the gas engine with manual and crew cab. The only way to get the manual and crew cab is to go diesel.

The lot I bought the truck from got it at an auction in Texas. It's exactly what I wanted, I honestly didn't know it was available till I found this one. I was skeptical on the transmission until I saw it with my own eyes (no pictures of the interior on the autotrader ad). A lot of the other trucks I had seen listed the Allison 6 speed as an "maunual/automatic" and that's what I was expecting to see in the truck.