Dynos measure the torque the motor produces down to the wheels and then from there horsepower is calculated with the formula: hp =
(tq * rpm )/5252.
300 bux to run your truck is a JOKE. Shops charge about 100-150 an hour to DYNO TUNE your car or street tune it not strictly for pulls. Last time i went i got 5 pulls for 60 bux. Usually its about 75 for 3 pulls on the dyno with time in between to modify something if you want.