2005 2.7L Prerunner modifications

Trade it in for a 6 cylinder model.

I have a 2.7 Taco and if you look at the specs they are pretty much state of the art - twin cams, injection, variable valve timing, etc. For towing you probably want a fat torque curve which the truck already has. It also has a pretty good sized exhaust. My guess is that the engine is really close to optimum for a ruck engine, meaning you would have to do something radical to it like a turbo to get more power without compromises elsewhere. IMO the 5-speed doesn't have enough ratios, a 6-speed might help if your truck doesn't have it already.