2007 Ford Truck

Transmission problem
2007 Ford Truck V8 Four Wheel Drive Automatic 45000 miles

Got an 07 Ford F150 FX4, it came from the dealer customized with a look alike sterling package on it - with a 6'' lift and 35 /12.5 r17 tires on it. The truck has 45000 miles on it and the transfer case is leaking transmission fluid and when you pull off you hear a whinning noise through all the gears until it shifts into the passing gear, then it stops. We have only pulled our 87 buick T Type Turbo with in 3 times to the drag strip. Whille pulling the car it strains really bad. What could be causing this or what can I do to prevent any further damage? Wonder what that noise is coming from?
August 26, 2010.

Where is the transfer case leaking, a seal, gasket?