Lou,
With your truck I doubt you will get close enough to the cab without backing. The GM's just don't have the turning radius.
When I picked up my truck I did try it out with the u-turn stuff, and the 90 degree turn. There is no way I would have been able to make a 90 without the slider. Look at the pictures I posted.
After my first "turn around" in a parking lot, which I did just to try it, I decided I will try and avoid those maneuvers if possible. It really torques up the axles and tires. I would guess that the center line of the front tire to the rear tire was at least 6-8 apart from the "scrubbing".
If you want to practice, which I suggest you do, find a gravel parking lot. That is where I played around with the tight turn stuff (at Mor/Ryde).
The gravel allows the tires to slip and stay more in line.