Transmission slips when shifting from 2 to 3 going down hill.

[Chip]

Descending a steep grade, in low range, with a automatic transmission if you shift up into 3rd gear manually the transmission seems to just let go and then catch, with so much force it knocks my dog off the seat. I've got the Adventure Package with the low low range. Is this just normal or is it the beginning of the end?

[f5fstop]

Are you in 1st or 2nd when doing this shift into 3rd? I'm going to guess that it might be normal, but haven't tried it on this vehicle.
If in 2nd you are jumping from 1.625:1 to a 1.000:1 trans gear ratios, and you have a 4:1 gearing in the t/case. So, the jump could be due to the higher gear you manually selected.
I'll give it a try in a few weeks out in Moab, maybe I can wake my kid up.

[f5fstop]

Are you in 1st or 2nd when doing this shift into 3rd? I'm going to guess that it might be normal, but haven't tried it on this vehicle.
If in 2nd you are jumping from 1.625:1 to a 1.000:1 trans gear ratios, and you have a 4:1 gearing in the t/case. So, the jump could be due to the higher gear you manually selected.
I'll give it a try in a few weeks out in Moab, maybe I can wake my kid up.

(Let me make note, I'm not a trans expert; not enough electrons running through the case for me.)

[Chip]

It's doing it when shifting from 2nd to 3rd desending a steep hill. It's not the smoothest shifting truck I ever had but it is really a low ratio transmission which may have something to do with it.

[DWPC]

I'm guessing, but I think your expecting the clutches in the trans to do something they weren't designed to do; upshift under "negative" torque from engine braking. OTOH, if you weren't supposed to do that, the ECU should have been programmed to prevent shifting in that condition. Or maybe the Hummer folk just didn't anticipate it. I never upshift going downhill in low range. If it starts sliding, I'd apply power. At least thats how I'd have done it in my old Montero; I haven't had the H3 in that situation yet.

Too high a gear when going downhill may leave you with no engine braking and too much RPM to downshift while keeping traction. I'd be interested in knowing if any 4x4 w/auto can do what you want to do.

[Chip]

That's what I'm doing is using engine breaking and I'm shifting up when the grade reduces. I've had two speed transfer cases in other trucks including a Jeep Rubicon that never seem to let go like that. It just seems it can't find the gear, free falls and when the gear finally engages it slams everything forward, enough force to set my dog flying into the dashboard. Bear in mind it was a really steep hill.