Dave,
It is imperative that you RTFM (Read The er, 'Fine' Manual) for YOUR
vehicle. My Dodge w/Cummins is OK to tow in OD. The THM 700R4, as used
in GM's half-ton vehicles (at least until very recently) required towing
in Direct, never OD. What is OK for one may well lead to an early death
for another.
<<Jim>>