Motor mounts might make a difference in clutch free play, but not cab mounts. The pedal shaft is mounted to the frame, so the cab position has no affect on clutch adjustment.
Your clutch test sounds about right.
I've had a clutch that wore out on a truck and could hammer the go-pedal in high gear going down the highway and have it slip. Of course drag racing the truck couldn't have had anything to do with that, right?
