all stock trucks suck at 40 mph... reason is your out of your power band, and it takes a little to get the rpms to rev. Same thing at 80mph, I tried an 80 roll run against a vette and my window switch woulndt even spray my nitrous because I wasnt at 3500rpms. so I looked stupid. by the time it sprayed the vette had allready slowed back down.

IMO dont do 40mph races. 30mph and 50mph are best.