I live in the U.S. and I have a 1999 Viggen.I'm going to upgrade the ECU to either a stage 2 or stage 3.Which is the way to go? I'm also going to add a 3" exhaust system,bigger intake tube and a opti-flow air filter.Also why does Abbott only make a 2 1/2" exhaust systme and not a 3" system.