in my two 51's, a gmc and chevy both are vacuum. shift mechanisms are different and located in seperate locations. the shift chambers and the rears are different but they both work the same way. i live in mountanious country in eastern pa and i use my trucks, so knowing how to shift up and down is a must if your ever going to get somewhere. what i have found is that by tapping the clutch while upshifting the rear will make it a smoother shift. when downshifting the rear while going up a hill i find that just before hitting the lug stage is to shift the lever and take my foot off the pedal and press it back to the floor. during that brief period it shifts. timing has a lot to do with it. for instance my fire truck weighs the same all the time 11,000 lbs. the shift point are always the same. with the dump they are not depending how much weight im carrying at the time. maybe the difference is that one has a 270 and the other one has a 235
but thats how i work them and how they work for me with the least amount of blown shifts while downshifting.
for splitshifting then you need to use the clutch because your changing the transmission and the rear takes care of itself.
i dont advocate trying to downshift the rear while your going down a hill either like you would the transmission. that is unless you want a new experience in how to make strange noises from you truck
