my 2001 Tahoe has steering issues, while in a long sweeping turn, the steering will just "lock up" for lack of a better term. very scary, and if you fight to turn the wheel it will turn loose and then you have to jerk it back fast to keep from crashing
fluid level is where it is supposed to be
no leaks, new belt
what else can I check???

 

can this condition be repeated while the vehicle is not moving? I don't know alot about the steering but I would be checking the steering knuckles and inside the column.

 

I know on my 97 Tahoe I had an issue with the speed sensor for the steering, that was to make the steering more sensitive at low speeds but when it went out it made high speed steering super over sensitive...
There is a sensor on the steering column that was replaced, I don't know if that same sensor has any bearing on your situation...