Well I assume you have a 3:73 axle ratio, and it should be 4:11, or even 4:56. But you have two differentials to change out, which can be a little expensive. Your other option would be a "GearVendors" or "US Gear"underdrive gear box behind your tailshaft, but it will only work in 2 wheel drive. Now your looking at about $3000.00 till your done with cutting the drive shaft etc. Do you have a lift kit that changed the driveline angle? That would be a problem when adding the "GearVendors" You could look to swap differentials with a salvage yard, or someone looking for better mpg. Lastly, you could go back to 245 tires , But I guess you wouldn't want that.
Tom McCauley (DP Member #513)
"Tankers-ToyII" Loaded 05 D/A K-3500 CC, SRW. Deep pan on Allison w/Transyn. Edge Juice w/attitude, 4" Kennedy exhaust, 98 Gal. Transfer-Flow cross bed fuel tank, Leer 100XQ bed cap. Reese 14,000lb class V hitch w/ dual cam HP sway control. Tow 34ft. 32FKD Holiday Rambler travel trailer. GCW 20,360lbs