Does anyone have any info / experience with the 4 wheel steering trucks??? How much are they? fully loaded crew cab/DURAMAX. Is it worth the money?

I have test driven the Sierra Denali that has this standard. It is a longbed half ton with an extended cab. The truck handles supurbly for a truck. I did not tow with it. I only think it is available on the half tons, and suburban 2500 with the 6.0. I have not seen any indication you can get it on a 2500HD with D/A. The rear Dana axle of the 4WS only gives the Sierra Denali a 10K tow rating, so the D/A 2500HD pickup would lose some tow rating if they go to this as is.