2002 Chevy Tahoe Steering feels like its "locking-up&a

The steering wheel feels as if its "locking up" at times when either just driving (I'm not anagressive driver) down the road and am turning into a curve (no braking at all) in the road ahead or when I first noticed it about two months ago when braking hard and trying to steer to the left. It seems only to be noticable when turning left. Either at speed trying to make a curve or when slowing to turn left. Although I don't notice it nearly as much it sometimes feels like its starting to do it when turning right now too. Any suggestions on what to look for before I crawl under and start tinkering myself? Also, Where can I get a good service manual(s)? For this thing as I plan on keeping it till the wheels fall off! (I bought it new)