Need help: Fith wheel to high with 11R/24.5 tires

2009 pete 386 48inch midroof flexair 3:55 rears cat C-15 475 HP 13spd 230 wheel base. Ya think i'll get 6mpg out of it? won't be cruising faster than 65-68. The company's Qualcom police bag you anything over 70. i'll look into the 5th wheel height when I get it back. looking at 90% tread on the 11R 24.5...49" FW....hate to have to buy tires already but that's my own fault
Ok we're getting close....I read that I can leave the steers alone and swap the drives only from 11R's to LP 24.5.
Lower Fw mount.......If I get it down to 48" can I stop bitting my nails everytime I come to a 13 6 underpass?

Thanks,
GP

 

Holland 5th wheel

 

So whats it gonna cost me to re spec this truck to lower down from a 49" height FW down to 47"?...can I straighten out this problem spending less than $3,000?....cant afford to change the rims down to 22.5. so it has to be LP 24.5 and a 5th wheel rework(though the Fw does not look high on the frame).
Thanks, I really appreciate all the input so far
GP

 

This is the truck I've been talking about. dont know if the image is large enough

GP

 

You have point.maybe that's what i'll do.get it home first .
Thanks,Gp