The 400 is a much tougher transmission than the 350, which is a good thing. You'll need a momentary-contact switch at the carburetor for a kickdown if you choose to run one. Otherwise, just drop the shift selector down one notch to D2 for a forced downshift. Downsides- - - -the 400 is considerably heavier than a 350, and it consumes a little more HP to keep the gears turning. On a vehicle the size of yours, the power loss won't be noticeable at all. The 4L80E is the overdrive version of a 400, but it needs a dedicated computer and a bunch of electronic inputs to make it work. Big $$$$$ for the privilege of having an overdrive!
Jerry
