. Hi Chris, it's nice to see another 4bt fan, and we are not far from each other! I am using the th400 auto that was origanal behind my 4bt. I drove it up and down the street today for the first time with the nose off. Holy $#&T it's got power, but it still has the origanal rear end with 4.10 gear think I'm going to need something like 3.07 gear to get hi way speed. Probably a jeep cherokee rear end. I am keeping her with the manual steering and drum brakes. My intention is to make my truck look like it was born with a cummins.