ice cream man

well i put a stall in my high mileage 60e and it didn't last one day. im getting a local guy to build it for me he is well known and i have first hand experience with his trans builds. well long story short he said no matter what he did the tuner had to be dead on for it to hold so can anyone give me a start to what i need to do in my tune don't want to waste all the money and time a second time