Not much unless you want to re-work the entire front end. There is no way to disconnect the hubs from the front driveshafts. So even if you remove that all of the rotating mass in the front is still all rotating and causing drag. This has been discussed many times before...

 

There is a mod for the TC to convert it to 2wd . I dont know whats invloved but still I agree with mixman the shaft will still be connected to Front dif .
I love the full time 4wd
But also I wouldnt trust such a heavy vehicle in 2wd since it wasnt designed for that purpose

 

You will not get better gas mileage without the front wheels turning. These things are beasts and need all 4 wheels with power to get it up and moving. I know because I was having issues with my TC and buttons for a while and drove with the front disengaged and the gas mileage and power was incredibly terrible.