I have a commercial 2004 GMC 350 flat bed with the 6 L and 4l80E very similar to the Sierra 350. Might even be the same, if you know the dif let me know to please. Anyway I would like to put in a switch so I can lock up the transmission TC. If you know how please let me know. I drive a lot of small roads at about 40 to 45 MPH and it just never locks up correctly. Made to lock up around 50 something and I just never get there. I'd also like to use it to help on the down hills too.

 

So you wanna save some gas and have some engine brake too?

 

Why not if it's simple to do? Makes sense to me.