[Accelo]

Let me see if I understand this correctly;
Both the thm350 and the 700R4/4L60s use the same PRND.
PRND21
PRND321

The first gear is just further down on the column.
This means they both should be able to activate the NSS correctly.
I am just guessing the ratio between the column and the shifter on the transmission has changed and is not the same ratio as the factory designed it.
This could make the switch not index correctly.
Just a guess.
Cheers