While trying to pull a buddy out I decided to put the T-case in 4 Lo thinking that it would have more balls. Wrong! The motor would just rev to about 2000RPM and the truck wouldn't move. Moving forward was no problem but reverse was outta the question. I ended up putting it in 4 Hi and giving a big yank. Anyone else experience something like this?

Are you saying the wheels didn't turn in reverese?

Exactly. Once the rope was tight and I went to mash the go pedal she went nowhere.

Sound like a serious powertrain problem if the low range doesn't engage. Do you have a manual shift tranafer case?

Sound like a serious powertrain problem if the low range doesn't engage. Do you have a manual shift tranafer case?

:exactly:

I couldn't agree more - sounds like something is not engaging. If I did that with my 6cyl Blazer it would break something or stoke the tires.

Thats interesting that someone else has experienced that problem. My dads 01 with allison does the exact same thing when you try to back up a steep hill in low range, if you hammer on it, nothing...untill you put it back into hi range. My 02 has as the six speed and I don't have this problem. We never did take the truck into GM to have them look at it. To tell you the truth we haven't been into another situation where we had to use low range in reverse, I think he likes to be in 4 hi ever since the incident occured. Let me know what you discover.

J-HEFF

Just out of curiosity, did you rock the truck just to make sure that it locked in?

William

It is normal. Engine RPM and torque is limited when in 4LO and reverse at the same time to prevent drivetrain damage due to the torque multiplication. There was a bulletin about it when they first came out but I can't find it now.

Thanks Sid. I thought something was wrong with my girl.

hmm. seems like they would tell you stuff like that when you buy one of these 45K trucks or at least mention it in the manual.

If you are not supposed to be able to back up in 4-Lo, my truck is broken. I put mine into 4-Lo to back my 11,000 lb 5th wheel up a very steep driveway (8" rise over 48" run=16% grade). With my foot off the brake, the truck just idles its way up the hill. I don't think I'm going to go to the dealer and have the TSB applied. If I did, I couldn't park my trailer!

It is normal. Engine RPM and torque is limited when in 4LO and reverse at the same time to prevent drivetrain damage due to the torque multiplication. There was a bulletin about it when they first came out but I can't find it now.
It seems like there was an ECM update for the '01s that gave you some of that low range torque back. If it is limited so much that the truck wont even move, it is not even close to hurting the drivetrain. If your trucks have never been updated, it would be worth complaining to the dealer.