Allison transmission

GMC-GET-R-DONE · July 1, 2006

I just purchased a 2006 2500HD GMC Sierra and now have 1100 miles on it. I have read the owners manual and the seperate Allison and Duramax booklets. I love this truck. It rides much smoother than the 93 K3500 dually that I had till the 6.5 let go a month ago with 180,000 miles. It was leaving clouds but still got us the last 100 miles home. GM products just don't die!

Anyway, this truck has options that I never had before when I tow. My first question is when do most of you use the "M" and when do you use the Tow/haul button?? I guess the manual would have made more sense if they had used examples. We have very twisty passes over here with corners speeds of 20mph or less and 6-7% grades. Before I tow horses or my tractor I want to know what I am doing or they may end up in the back of the crew cab. The dealer told me not to put on a trailer brake unit because the truck will do it all so I guess a little help from anybody would help. I kind of think that the M is for pulling passes so that the engine is not always shifting up and down and T/H is for going down so that the engine and trans slow you down?

My second and last question is since I steped down in size from 3500 to 2500 the ride is much nicer but when I put on my tractor hauling trailer and tractor the truck squats a lot (3" at least). I could take care of the problem with a load leveling hitch but has anyone used the airbags that take the place of the spring stops. If you have were you happy with them and what brand.

Trouttrooper · July 1, 2006

Dealer is full of horse caca. Put a brake controller on, you still need to be able to control the trailer brakes. T/H mode will ASSIST in controlling speeds when going downhill by automatically downshifting to a lower gear. There is nothing magical past that.

The only times you would really need to use the manual mode is like you said, keep it from shifting up and down as you go around tight curves up a hill. Another case would probably be going down a really steep hill when you don't want it going past 1st gear. The other 99.999% of the time the Allison will most likely take care of itself.

Just got back this afternoon with a load of hay. I've got one windy 6-7% pass 3 miles up and 6 miles down the other side with the load (total trailer weight approx 9,000lbs). The uphill side I forced it to stay in 3rd for the really windy part. Other than that I had it in "D". The downhill side I tapped the brakes a little at the top and it downsifted itself to 3rd and then 2nd a little later. It held itself to around 35 mph all the way down, didn't have to use the brakes at all. Once at the bottom I stepped on the gas and it shifted back into 5th and away I went.

Cant' help you with the airbag question. My 3500 SRW has 7 springs, don't need any help

GMC-GET-R-DONE · July 2, 2006

Troutrooper, thanks for the reply. I really like this truck and that helps. I didn't think the dealer was right about the trailer brake but they said it would mess with computer system that contols the engine and trans.

I must say on there behalf that the price was right. The truck had 16 miles and we paid $36,500 for it off the lot. While we were there the lady was making reservations for a couple to come up from Texas to buy a truck.

Thanks again. Have a good fourth