I have to agree with esh about airing down my 33/9.50's, not a good idea
As for gearing, I had to change mine over to 4.88's to get back to factory spec's (FJ 62), original tires were only 28's. 33's through off the speedo and odometer by about 17% as well. Now my rig runs 60mph at 2300rpm, which is fine with me. one note, my stock auto tranny has an overdrive. I don't think 4.88's would be a good idea without overdrive if you drive the rig on the road.
If you go to tlc4x4.com you will find a spec page that lists the factory height of your rig with stock tires, compare the height and it should tell you approximately how much your springs have sagged.
Good luck