Fifth wheel height

Your drives are 315?
I can see your steers being that but very odd choice for drives.

There are different size stands that go under your 5th wheel on top of your slider. You can order different heights.
But first check there is enough clearance before ordering and installing. Could be anything from frame height to tire size or 5th wheel? Or a combination of all the above?

 

Are your drives duals? My guess is they are 9” wheels never seen 315 on drives. You’ll have to take a look. Should be stamped in the barrels?
315 is one and a half inch taller than a low pro 22.5 (295 22.5) so that’s not going to gain you buy 3/4 of an inch.

 

Changing to 275/80R22.5 tires will drop your fifth wheel height by 1 inch.
Your fifth wheel may be on a high rise mount, and a low rise fifth may drop your total height by a few inches.
Trucks can be built for different applications and you seem to have bought a truck built for different purpose than what you want to do.
You can adapt it but it may be expensive.

 

You can reuse the plate . But it’s gotta come off to get to the risers.....