We can only guess what gearing you have without more info. Some have 4.10's, some 3.73's, and some even 3.55's I think.
Get the axle code from the drivers side door jamb, or even better, read the metal tab on the rear differential cover. There should be a metal tag on one of the bolts holding the differential cover on, should have info like "8 8 3 L 73" or something similar. Let us know what it says.
I recommend against using those crappy "coil-overs" because the shock mounts aren't designed to carry weight, they most likely limit suspension travel, and give a stiff ride. Warrior sells a shackle (WAR-153) that gives 1.5" of lift in the rear, no decrease in ride quality, and allows the springs to move easier.
I run 33x12.50's on 15x8's which required small fender trimming in the back of the front fenders. A torsion twist will make the ride more stiff, and you will top out the suspension constantly on small bumps. There is only about 2.5" of downtravel in the stock suspension anyway. If you raise the front 1.5", you only have 1" of downtravel left.
However if you want the truck to ride like crap, you can probably get about 2" of increase ride height, but be prepared to replace balljoints and cv joints quick and have a rough ride over small bumps in the road.
My sport trac came stock with 4.10 gears, and I didn't like it much with 33's. Pulled okay but the engine and transmission had to work a lot harder on hills, and especially any time offroad, I had to use 4-low a lot. I re-geared to 4.88's (slightly overkill), but the truck stays in overdrive a lot more, and it pulls much harder. 4.56 would be ideal with 33's, I personally would go anything less than 4.10's with 33's though.
3.73's will get around but not very well, and your (already weak) transmission won't be happy for long.
lol
