Shifting from Overdrive to 3rd gear WHILE driving?
 

Hi all,

1995 K1500 automatic, V8 5.7L
I have a lot of hills in my area and the manual states to not use overdrive (FYI, I only have the D with the circle around it) and to use 1,2,3rd gear, whichever fits the steepness, but what it doesn't say is if I have to come to a complete stop to do this.
It is sort of a pain to pull over before/after every hill to change gears.

So I was wondering if anyone knew if you can switch from overdrive to 3rd gear, 3rd back to D, 3rd to 2nd, 2nd to 1st, etc etc...WHILE driving the truck.
Part of me thinks you can't because, you know, it's not like you can switch to R while moving; that's bad. I mean, how would it know to engage the clutch? Wouldn't I have to push the brake down to change it between gears? Also what if you accidentally go from D to 1.
Who knows, maybe they put some safety features in to prevent that, or maybe it's not possible at all...
Thanks!

- Chris