What is the REAL maximum HP/Torque that can be put to a RTLO16913A ?

I can't find any info from any real source, I know... I know... 2050 pounds of torque, bla bla bla... I hear trucker stories about blowing up transmissions but right now I'm at 2800 pounds of torque (725 HP) to the ground and haven't had any issues with heat or anything else. Im at about 50K miles on the motor so far and ready to bump up my tune (still running the "break-in" tune). My question is, does anyone have experience with 3200 pounds and 900 HP using a stock transmission and rears? If so, were there any issues and what gear oil do you run, how often do you change it, do you run any coolers etc? BTW, Im in Phoenix AZ (hottest place on earth and we're in a valley so everything is up hill).
BTW, I was told by a guy who has built dozens of 13/18 speeds that the guts are mostly the same (with a few minor exceptions) in 13 and 18 speeds. He said the 18 speed is not really any stronger than a 13 in high range. Is that true?

 

Since two people said 725 HP doesn't add up with 2800 pounds of torque, I'll address that... The dyno guy at Kenworth in Phoenix showed the instant hp and torque numbers (peak) and I was shocked because torque was 5500 and change! WOW! He laughed and said "thats because we pull numbers from both rears" I had to divide by two (I'm not very experienced with dyno tuning big trucks). So, the reason I said 2800 was I just divided the 55xx pounds by two. If thats not the correct way to do it, please explain.

 

Not much to show ( I run in California so no smoke ) but I tried to make it purdy.

 

So, 550divided by 3.36?

So, 5500 divided by 3.36? Thats only 1600 pounds, my truck absolutely runs away from stock 550 HP Cummins all day long. I mean when they're doing 30 MPH up Sunset Point grade out of PHX, I'm doing 55 MPH... So you're telling me that I run almost twice as fast as a stock Cummins and I've only got 1600 pounds of torque?