Figure it out before driving more...
I can't quite sort out what the problem is from the description, but stop driving it until you figure it out
This would be a good time to check out all the steering components anyway.
1. With the engine off, is there play in the steering wheel? If not, good. If yes, find it. If the steering wheel moves and the Pitman arm at the bottom of the steering box doesn't move, then you have a worn steering box, intermediate shaft, or steering column bushing/bearing.
2. If all that is okay and the Pitman arm moves, then raise the car (don't forget the jackstands) and check for play in the center link, idler arm, tie rod ends. If you can turn a wheel in and out and feel looseness before the other wheel moves, some or all of those things are worn, or the ball joints as well.
3. Grab the top and bottom of the tire and try to rock it in and out. Any movement likely means worn/misadjusted wheel bearings
4. Turn the wheels all the way to the left and then the right, and check for play in the linkage or ball joints.
5. Now, onto the variable effort steering. If the boost is suddenly increasing in curves, then the valve is at fault. It's supposed to give you full boost at idle and less as the car's speed increases. You can disconnect the electrical connector and the problem will go away.
If this kind of analysis is straightforward to you, great. If it sounds like a bit much, then bite the bullet for a diagnosis fee and take it to any Chevy, Buick, or Cadillac dealer and have them show you what they find. Don't risk lives with messed up steering