Transmission not holding back on downhills

Recently bought a 04 Avalanche one owner 95,000 mile. Really like this vehicle. Came home from camping Sunday. Pulling a 14' enclosed trailer with 2 dirt bikes in it. Have a 2 mile downhill, had put transfer case in 4wd low range to help with braking. No matter what gear transmission was in, if you let off throttle and RPM's drop to about 1,000. Hit accelerator and engine speeds up to where it catches up with  transmission. 2wd, 4wd, in or out of tow mode no hold back. Any ideas. Thanx, Forest

4LO is only meant for a MAX of 20mph. And you can only shift into it from a stop or ideally going 1-2 mph. Anything more and it won't let in engage. I don't know for sure... Hopefully someone else can chime in.... But my guess is it was doing weird things to your transfer case...

Also you would be better off shifting your transmission to 3rd... Not using 4x4...

Sounds like your override clutches are not being applied or are worn out.  They aren't usually the first ones to go.  Could be a sticking valve in the tranny valve body.  I suggest you consult with a tranny shop.  Valve body can be accessed without removing the transmission.  Clutches would require dropping the tranny.

enoniam said:

Sounds like your override clutches are not being applied or are worn out.  They aren't usually the first ones to go.  Could be a sticking valve in the tranny valve body.  I suggest you consult with a tranny shop.  Valve body can be accessed without removing the transmission.  Clutches would require dropping the tranny.

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Well it's in tranny shop. No codes. Computer is sending signals to tranny, it's not following orders. Could it possibly be female transmission? Thanx for all the info, it was helpful. Donations for repair can be texted to 1-800-who-cares. lol Forest

UPDATE! You ain't gonna believe this. The reason the tranny is not holding back is because there are NO pistons to operate the override clutch- clutches. How lucky can you get. That's what the tranny shop told me. Well at least it only cost $2,250 and I don't have any worries about transmission failure. Thanx for the help guys, Forest

I wonder if what they meant was that the seals on the pistons were shot and hence the pistons weren't operating.