I dunno,I havent seen anything like what your talking about,Looks like its either take a loan out on the house and buy that radio system,or get that thing,I forget who makes it I think maybe venom rc or something,but it just takes your highest speed,so if you made some kind of adjustmest you will be able to see if it made it faster or slower.But it doesnt transmit it back to you,you just have to drive the truck back and look down at it.
I think that would be perfect,I would think looking down at your radio watching the MPH grow,you would hear a smash at the other end of the parking lot by not paying attention.
Or if your dead set on watching it by remote or something,buying a radar gun and just setting it up near you would work,and it would read out how fast your going and probally save the highest speed.But im sure a good would run a good bit of money,,Look ebay..Hope this helped