power loss in drivetrain

Let's say you have 500 flywheel horsepower, how much rear wheel horsepower will that be for a Duramax 4X4?
Some techs say 45% drivetrain power loss and I figure that it is too much, I figure it may be around 30%?
Does anyone know how much power loss before you get the calculated rear wheel horsepower?
My Bully Dog monitor shows 356 horsepower with the 285 tires and 426 horsepower with the 245 factory tires. Is that rear wheel horsepower?
Numbers may not be too accurate but I can feel more torque and power with the 245 tires but spins out too much in 1st, 2nd and 3rd. ET's was 14.7 on the asphalt, knock off 1.5 seconds for the spinout and that is with the 245 tires but did 15.5's with the 285's and gear ratio is reduced with the 285's but with the 245's the gear ratio is factory 3:73 gears, have not tried the track yet but will wait till the motor breaks in and loosens up at around 8,000 miles. It should be able to run 13's on the track, hopefully. That is pretty quick for a crew cab 4x4.
Bad Max

Back when they first came out, GM advertised 300 engine hp. They pretty much all dynoed 240 rwhp. Thats a 20% loss.