Holler out for the diesel Doctor in Mt Vernon,Il. For $100 he'll mess up the ECM and remove the parameters. If it's your truck - have at it. If it's a company truck, wait till your boss finds out, and then research the "Got fired, looking for a job" threads, or the "I rolled the truck, what now?" threads.
Lol, This subject comes up alot. People seem to think of a governor as a physical thing and don't realize how computer controlled the truck really is. As for making it go fast, Yes it can be done. Buy said Prostar then take it to the dealer and have the governor turned off and Profit.
I'll take a wild stab and say it's a company truck. Let's say you fool with the ECM, wreck it and kill someone. Books will be thrown at you from all directions - and your company won't be taking all the responsibility - Learning some "left door closed " tricks may benefit you more.