your auto will not hold up... mine went out with that much HP/ TQ. had to change over to a TR6060. in all the research i did, there was nothing concrete out there that was tested and everyone said the same thing.. "wont last and dont spend the money on stuff that will fail" I wanted something that i could drive on the street and have no complaints/nor worries if i could get it back home.... so i OPTED not to build the auot, to many variables...
just sharing what i found and good luck with this other company. hope they have a year or two with the parts on the road.
For that HP you are looking for, then you have plenty of options... the 4R70 or the TR6060 is the most popular....
I was running around 600 hp crank, and my 5r55s was holding up, so far; it was 'upgraded' as well (servos, billet input shaft, internal upgrades). But I didnt want to push it farther and tear up a perfectly good working trans with the power I was adding. Opted for a 4r70...just DONT GET ONE FROM LENTECH!!!
PA doesnt even rate their 5R above 500 to the wheels.
I am not touching my auto, and will be making 550-600 soon. I will run it and if or when it breaks, I will just go for a 4r70. No point in upgrading the 5r when above 550rwhp.