Many folks ask about installing a TH400 or even a 350 behind a 6.2 or 6.5 that had an electronic box before.
The trannies will usually swap in fine with minor things such as the flex plate to deal with and maybe an adapter for the input shaft or the center mount.

All the vacuum modulated trannies require a **control valve** that bolts to the injector pump to control the amount and timing of the vacuum to the modulator. (Must have a good working vacuum pump either the rear mounted one or a belt driven one)

** The GM part number for this little creature is 14057219 andf can be ordered from your favorite GM store.**

Many countermen/women dont have a clue about this little valve or even what you are talking about when you ask.

This valve will work to run either a TH350 or TH 400 box with the 6.2/6.5 diesel.

Robyn