What can be done to increasethe power on my 1991 3.0L 4runner?

You could add a cold air intake, most companies advertise a 15% or more power gain.

companies advertise a 15% gain....thats at the crank in optimal conditions after a tune. slapping on a cai typically is good for 1-2 hp. not worth the money imo. theres really not a whole lot you can do to it without dropping a lot of money. whats the budget?

Rocket boosters, skateboards, and a lighter... (And duct tape)