Navistar pretty much has the market cornered on class 5/6 trucks. The closest competitor would be freightshaker I guess. The maxx7 and the dt466 still make good medium duty workhorses. Straight box trucks. Penske uses exclusivly durastars I think. Maybe terrastars. Cant remember. But you have good light trucks that have good drivetrains and good engines and give you a good ride so you can adapt them pretty easy to do whatever you want.