when in 4WD my front end begins to wander as if the tires have a mind of there own, almost like there is alot of play in the front end. what could cause that?

It has done this ever sense I had the truck but the previous owner said it was a new problem. It does feel like the front end is trying to escape because it'll jerk really hard from left to right.

I was a master mechanic for over 17 years before I left the business. My son has a 1991 s10 blazer. I checked the front end and found excessive play in the idler arm. You can move the right or left front tire side to side over 4" and either side is not affected. That is unacceptable and causes tire cupping. I told him to replace it without looking at the actual structure of the part itself. After he replaced it the same sloppy conditions were present. With my bad back I looked at the replacement part to find the side of the idler arm that attaches to the frame is the ball type causing the slop. Obviously a manufacturer flaw in the suspension. In conclusion there is not a damn thing you can do about it. You are not crazy and its just not normal. I am now in the hunt for an old school idler arm with a bolt holding the frame side of the idler arm that only allows left to right rotation and eliminates the up and down play in the steering system that is causing tire wear on the right side. If any one else has an answer or if I have been out of the business too long and the front wheels are now suppose to be able to not move in unison please let me know. being a GM certified mechanic I am embarrassed I did not notice this on the line. But then again that is what flat rate does to a tech. LOL