Welcome to iRV2.
Most ball mounts are adjustable by removable bolts for both a height setting and for the angle for the bars. The height needs to be set so the trailer sits level when hitched to the truck with the bars cinched up.
The angle setting will raise or lower the ends of the bars.
'11 GMC Acadia SLT AWD
'11 GMC Sierra 1500 4x4 Extended Cab