With the latest update (1.34), I've noticed that the truck surges when going over bumps. It acts as if a turbo or nitro boost has been activated. This only seems to occur with the 6x4 chassis when hauling a trailer. Without a trailer, it behaves normally going over bumps. As far as I can tell, the 8x4 doesn't have this problem. I haven't tested the short chassis configurations.

Correction: The 8x4 chassis is affected as well.