regarding the trucks that have it and those that dont, , if youre running a cat, the cat on the truck with air will last far longer than the one without. and as was stated, the engine will be much happier. it also allows the engine to run a richer fuel mixture at the engine (which would produce better performance) because the air injected into the exhaust, burning the leftover fuel, will read as running leaner than an engine without the air injection which would register as rich, and cause the computer to pull fuel.
and yeah, getting the old air tubes out are a PITA, but then again, thats all exhaust system work, the heat and corrotion cause everything to get very cozy with its neighbors.
funny thing about the air though, now that i think about it, if you were running a turbo, the air injection would probly actually help spool the turbo, because not only are you adding air volume, but the air burning the unburned fuel would cause the exhaust to expand even more and raise in temp, which would spin the turbine faster than an exhaust without air injection, so really, you could justify the air injection as a performance aid on a turbocharged engine.
