Quote Originally Posted by sherlock9c1 View Post
Huh. I assume nobody's discovered this? (where's steveo) I know the 4L60E itself has "abuse valves" in the forward and reverse apply circuits which bypass the normal apply process under heavy load conditions and provide much more power to the clutch applies to avoid slipping them during these sorts of applications. If those valves get stuck in the open positions in the bore (been there experienced that), you get really harsh shifts into gear from P/N.

FWIW, if you're stuck in snow, don't bother shifting. Automatic transmissions take too long to shift. Just use the gas pedal to rock the vehicle back and forth, but leave it in one gear. Worked every time for me when I was in the snowbelt.
I use 2nd gear start to rock it enough to move. No issue driving around with the limited ice days we have here. Can't stop people from doing dumb things so GM had to find a way to counter them.

I also seem to remember the older TBI PCM cutting timing if you manually shifted the transmission above the factory shift points. I guess the PCM saw that as "abuse"