Steep drive ways, at fuel stops can cause issues, even with 6"s clearance. It is better to hit them at an angle, than straight on. In some cases, crossing a roadway straight on, with the one you are crossing being higher, you can hit, with the truck rear tires at high point, and the trailer wheels still at lower area.
Sounds like your an aware kind of guy, so like all of us, you will learn quickly what situation to avoid.
Jerry