I have destroyed more transmissions than anyone I know, so maybe I can give a little advice! I munched 5 NV4500's (2 more were replaced before I bought the truck), 3 G56 g-speeds, and a few 48RE automatics. Never have had the chance to grenade an NV5600 though, yet. Knowing what I know now, I would have just payed the $6K for the Allison conversion and not the $6K I put into the 48RE. You didn't say what year you are working on, that will make a difference. I did tow heavy and often, but I would expect transmission behind diesel trucks to be able to handle what they were designed for. I would not use another NV4500 if it was given to me, and forget about a G56 junk Mercedes aluminum trans and dual-mass flywheel. If you like your automatic, put in an Allison and never look back!