4wd issue(truck bucks on turns)

my 1999 ford excursion has started to buck around the turns, like its in 4wd, its options are 4hi, 4low and AWD what do you think could cause this?the truck has 4 newer snow tires with studs on them, could that have anything to do with it?

check your idler arm and pitman arm for play in them and also look at the lower rear trailing arms, they may be rusted out at one end and you cant see it because the tire is hiding it