[Mike C]

All the keys do is re-index the torsion bar. They do the same thing as cranking the load bolt, they usually just allow more movement than cranking the bolt.

The IFS is designed to operate in a relatively narrow range, and moving things out of that can accelerate wear on ball joints, CV joints, and bushings. But no guarantee. GM used something like 3 or 4 different keys depending on the truck and its options.

So depending on what keys came in the truck and how high the bolt is cranked you can get out of the range of acceptable for all the front end parts. Obviously 4" is out of the range since those lift kits come with front diff lowering brackets and all sorts of other crazy things.

Cranking the torsion bar doesn't change the rate, just the angle at which the key is indexed. This is the same thing the new key does with the load bolt not screwed in all the way. The weight of the vehicle dictates how much the torsion bar twists so when you move the bolt up it causes the vehicle to rise since the same twist is on the bar.