2000 Silverado 4 Lo shifting problems

I have a 2000 Z71 Silverado, 5.3 with 4L60E trans. When empty or pulling a small trailer in 4 Lo ,the trans. shifts up into high or into O.D. and won't downshift untill it feels like it's stalling at 400 to 500 rpm.Once downshifted the cycle starts again. The problem exists only in 4 Lo and with the shift in 3 or 4 position and with the towhaul mode on. Anybody out there having the same problem and what was done about it.

It sounds to me that 4 low is doing what it is supposed to. You should only be in 4 low if you are in crap so deep that it's your last chance or if you are pulling a very heavy load a very short distance. It's not meant to go much past 15 - 20 mph if that.
The transmissions in the newer trucks will shift automatically if the strain on the transmission is to high. Example - in regular two wheel drive if you start out in 1st gear, and punch it, the transmission will shift whether you do or not around 25-35 mph. I have tested this.

Good luck.

Thanks for the reply. I'm talking 5 to 6 mph to be shifted into 3rd or OD. and to downshift at 4-500 rpm (near stalling) and the gas pedal at least 1/2 way down. The same thing happens on a not real steep hill on pavement and going straight. this makes it impossible to ease up a rough not steep hill or you can stay in 4 high ,work the motor and let the trany. slip. Not much of an option. GM agrees there is a problem but at this point are not willing to try and correct it. I have had many other 4x4 - auto trans. and have not run across anything like this before and have pulled my trailer over miles of rough going.

Not trying to be a smart ass but this is why i don't buy auto tranny's. That slippage in 4 hi under load you mentioned is only going to kill your tranny. This is also why road tracters are mostly stick especially heavy haulers, and why i don't put auto's in my hot rods i build. In a stick you just have to pick the correct gear for what you are trying to do. This takes some time to learn, but the equipment is much more durable. Jusyt my opinion but auto's are only good for citiy driving with multiple stop lights, other then that they can't handle extra carriculer activitie's well, like going fast or going towards verticle, partculerly under load. Jack