I understand the concept of the tow haul button, but I was wondering what actually happens inside the transmission when the button in depressed? Does it just lock out overdrive or something? What actually phyiscally happens when it is engauged?

Its all in the electronics. Nothing physically changes inside.

Push the button, go ahead, do it... I dare ya...

LOL, that will give you an indication of what it does. Raises shift points, Locks the TCC earlier, activates grade braking...

Changes the shift pattern, ie: makes it shift at a higher RPM so it won't be lugging, and makes the engine help brake almost like a "jake-brake" when you slow down.

It does NOT lock out Over-Drive. You need a mod to do that or an 04.5 or later D-Max.

Duff:

Actually '03s and up have the OD lockout.

i think it locks 2-5th gear. at least i think i read that somewhere.....

i don't know, i always have it on. one hell of a lot more responsive, like driving a standard- speed goes up with the rpms.

Duff:

Actually '03s and up have the OD lockout.
I stand corrected. Thanks for the correction.
:o

right on thanks alot,, diesel place is the bomb........