few articles or google 6r140
BTW the old 5R100 was a great tranmission and will take more power than an Allison. My friend has a modded Duramax and had to build the tranny to take the power from his larger turbo running 44lbs of boost. He is at around 550rwhp/900rwtq In a stock truck it is a great tranny with little or no issues but they do not hold power any better than comparative transmissions.
http://www.hsperformance.com/ford-6-7l-powerstroke-dyno-results/
497/1044 at the wheels with a tune and DPF delete