You'll want to do it in 4th gear, that is direct drive, 3rd gear gives you torque multiplication, and 5th is overdrive which reduces torque. Overdrive is for economy and that''s it, kinda why it's hard to find a trans with a double overdrive. As far as the hp and AF numbers, they should have a 5 gas analyzer to stick in the tailpipe for A2F numbers and an inductive pickup to go around a spark plug wire. No need to cut anything.