Is there a bar about 3 feet long that mounts from the rear end to the chaise?And how long have you owned the truck?
You need to change the rear shock that runs horizontally. I never seen a shock there.They usually have a sway bar. But you don't. Your truck is reacting like it has a broken sway bar. So I would change the shock. Good luck.
Thank you,
Jim
Chevy Mechanic
I HAVE OWNED MY OWN GARAGE FOR 30 YEARS.CERTIFIED IN ALARMS, CERTIFED IN AIR CONDITION.