Have run timbrens since my 98 Dodge 1500. They should ride at least an inch or so above axle housing. When empty.

Normal rear height,empty, is apprx 3" over front. My 31ft Cougar goes on and 2500 is just about level. At least headlights aren't hunting "possum" in the trees at night. Ride loaded is a bit stiff.
Did a 10,000 mile trip around the USA, last summer, no problem.