False.... the 5r110 will handle about 70hp more than an Allison 1000 of the same era.
As for the new transmissions, if anyone is familiar with H&S performance and their live dyno session "BREAKING POINT" you'll see that the stock Ford 6r140 transmission "slipped" at 884rwhp and 1660ft/lbs where as the new Allison (also stock) slipped at 568rwhp. While this sample size is extremely small, its hard to argue that every other transmission is FAR behind an Allison when the Ford 6r140 held 316 hp more on the same dyno.
However, the Allison 1000 has a big aftermarket support so they can be "built" bulletproof.
Best advice I can give to anyone considering owning a diesel is the advice that was given to me... drive all three brands with different options and choose which truck YOU like the most. But make sure you have a little money left over because I've seen 1 ford, 1 gmc, and 1 dodge sitting next to each other in a 3 bay diesel performance shop all getting head gaskets at the same time. I should have snapped a picture.