www.competitiondiesel.com/
They got everything on there.
Duramax is an awesome engine to mod, but the allison's are garbage. Once they are built, you won't have anymore problems, but it'll be expensive.
Cummins rules all, but same thing with the tranny.
7.3's are hard to get alot of horsepower out of, mainly because of the HEUI injection sytem, which can only deliver so much fuel. Of course, you could go totally custom, but that also gets expensive quickly. You want inspiration, search youtube for "Double Overtime". The ONLY powerstroke in the Super Mod class for sled pulling.
You can get alot more hp out of the 6.0's, and the 5r110 auto is pretty stout. You just have to do the EGR delete and get a MASSIVE radiator, plus a couple other things I can't remember. That info is readily available on powerstroke.org though.
Good luck!