tahoe 2007 4x4 front suspension problems

[PicoPico]

Hi, I have a 2007 tahoe LT 4x4, I noticed that when I drive it using only the 2x the front suspension feels loose and not tight at all, it feel very bad, it resonates to my steering wheel, as soon as I switch to 4x4 high or low the front suspension fees ltight and drives beautifully like new, the engine has almost 50,000 miles.

Every time a take it to the tyre shop for aligment etc, they never find anything wrong with it, but i feell it is something wrong with the front transmision.

has anyone had this problem and what was the solution?

thanks