[blykins]

Earl, I don't know if this is 100% correct or not...but it's the way I've been thinking about it. T-5's and T-45's are Borg Warner trannies...somewhat old school....but they're still making the T-5's. Tremec bought out or took over BW...and they're making their own trannies now. The 3650 is a 5-speed used in Mustangs...with an integrated bellhousing....you can't remove it. The 3550 is a regular 5-speed....and the TKO and TKO2's are improvements upon that. Like the other guys are saying, I think the TKO has a 26 spline input vs the 10 with the other trannies...and the TKO2 has a lower 5th gear ratio. It's called the Road Race TKO....I think they offer a Road Race 3550 also....not for sure about what's different though. Hope this takes a little mud out of the water.

BTW, have you ever thought about going the Toploader route?