OP wrote:
I put a brand new set of General Grabber ATX tires on the rear for traction if I ever encounter mud etc.
This can lead to handling issues when empty and especially with a trailer in tow or just carrying a heavy load in the bed.
Your OEM front tires may be a all season type tread which are great for handling issues vs a ATX with large lugs and large voids. They simply won't track the front tires like OEM.
Weight in the bed plus a trailer pushing the back of the truck around in hard side winds/curvy roads.......
New tires can have tread roll (sway) before their broke in....
To much or to little pressure can lead to tread roll.....
Once the tires are broke in I would play around with front and rear tire pressures.
If that doesn't help the issues then I would put the OEM tires back on the rear.
On every truck I have/had I buy a pair of wheels and have MT type tires mounted. That way I can get around in muddy worksites or out in my muddy/deep snow pastures or just to get out to a state highway (7 miles) during big s=now events.