how much power before trans starts slipping

[chevy12345]

I have a 2005 chevrolet 2500hD 4x4 duramax lly with the allison trans.I am wanting to put a chip on the truck but was wondering how much power the trans can handle before the trans starts to slip or give me problems. I have also just ordered 18x9 moto metal rims on 285 nitto all terrains and was wondering if they were goin to rub when i try to turn and stuff. thanks

[BMDMAX]

Don't go past 60 additional horsepower if you want your trans to be healthy.

285 what? 285/60-18's will clear with no mods but any bigger will rub.