If you are saying that the new tires raised the frame of the truck by two inches, that is a lot more than just one size bigger. Fifth wheel towing with oversize wheels/tires is generally not recommended, but I'm not sure I understand just what is going on.
"Can't raise" because of manual landing gear??? Again I don't quite understand. Crank it up!
More detail and/or pictures will help us help you.
Formerly posting as "littleblackdog"
Martha, Allen, & Blackjack
2006 Chevy 3500 D/A LB SRW, RVND 7710
Previously: 2008 Titanium 30E35SA. Currently no trailer due to age & mobility problems. Very sad!
"Real Jeeps have round headlights"