I've found applying the simple machine the PULLEY to winches maybe 2 or 3 times makes your force (f) equal to f=w(2^n) where W is the force of the winch and n is the number of pulleys used.
Like a block and tackle- take the cable, run it through a pulley, then attach the end to to bumper so that the pulley is the farthest point away from your truck. A hook or a cable the length of atleast half the first cable is attached. Then the hook at the end of that is hooked to the front of you truck also, with a pully with a hook or cable on it attched in the middle. It works GREAT, you can instantly turn an 8000lbs winch into a 16000, or 32000lbs winch. but i recomend you get stronger cable. It will go slower, but it will pull ANYTHING depending how many pulleys and how well you are anchored. A longer cable will also be necessar for long pulls. For instance if you took 3 pulleys, then 200ft of the winch pulling (a 400ft cable would be needed) the final pull is only 25ft. but it's worth it.