Originally Posted by 86Scotty
The quickest and easiest way is an overdrive button on the end of the shifter vs. the tow/haul button. I may have this backwards but I'm almost positive the 4r100 will have an tow/haul and a torqshift will have an OD on/off on the end of the shifter. Past that you'll actually have to read, research and all that stuff.
Definitely backwards, and also sometimes wrong
Gas engines with the TorqueShift (V10 for vans, also the V8 in some cutaways) have Tow/Haul mode with the TorqueShift.
6.0 PowerStroke vans all have the TorqueShift, but retained the OD-OFF light from the 4R100.
A better way to tell is just look for the "3". TorqueShift vans all have a shifter labelled "PRND321" except the new 6-speeds which get "PRND421". 4-speed vans have the traditional "PRND21"shifter