[Mr. Creosote]

TRD claims it gains a few hp. I would tend to believe them, however you will not likely notice improvements less than 10-15 hp using only "seat-of-the-pants" impressions. When I installed TRD duals on my Gen 1 it only improved a single tenth at the dragstrip. That being said, others have found these trucks tend to run very rich, both stock and when mods such as the duals are bolted on. Using some outboard electronics to lean down the air fuel ratio and optimize full throttle performance yielded very significant gains for some, which should make the additions more effective.