Hummer 2008 H3 Owner's Manual page 212

Design specifications required a minimum gradeability
of 60% (31 degrees) slope, with the vehicle fully loaded,
on high friction surfaces with maximum vehicle speed
not to exceed 6 mph (9.7 km/h). The vehicle is expected
to traverse this grade only for short durations. Never stop
and idle the vehicle or park it on this grade.
4-16
Also, your vehicle should be able to traverse a 40%
(22 degrees) side slope at 6 mph (9.7 km/h) while
fully loaded on high friction surfaces.