I don't know exacty how much torque you can get from a 22R but these are the things I've done to my 1st gen 4Runner to help with towing. It's a 3.0L but they really don't put out that much power compared to a well tuned 22R.

K&N Intake
Viper ECU override
2.5" cat back exhaust
OME heavy duty rear leaf packs
OME nitro shocks
Cross drilled front rotors
Green brake pads front & Rear
Class III Draw tite trailer hitch
Brake assist

I use 4 low to pull the boat out of the water and try to use the engine instead of the brakes on long grades.
Thats after I warped my stock rotors and smoked my 1st clutch of course.
have you tried it with your stock truck yet?
Might be worth just running around the hood (I don't mean South Tacoma) with your boat to see if works and going from there. Good luck, hope it works out.