ive got a 99 ecswb 5.3. i have an exhaust with headers , 3.42s and some other things. I am getting a trans built up with lots of goodies, along with a stall, and im installing an eaton with 3.73s. i am also going to eliminate that pos egr system. i want to get a nelson tune with some tm removed but i would like it before i put everything in, mainly to keep the tm from screwing up my tranny. if i get the tune and install it with my stock pos slipping tranny will it hurt anything? also what is the highest octane i could run with a stock thermostat?