Any competent machine shop can build a "Box" on the frame of the fifth wheel and raise the suspension accordingly. probably wouldn't go higher than 4 or 5 inches in this case but thats just me. Depending on the level and how big you are looking at 400 to 800 dollars. I have been involved in a number of "lifts" where this approach worked. I'm assuming you already looked into an axle flip in this situation so I won't talk about that. I raised my own 3 inches to solve the problem. Didn't want to do an axle flip so I went with the box frame underneath.