getting throttle body spacers

anyone know if i need to get a new air filter box when i put on throttle body spacers b/c i'm not sure if the stock one will fit on w/ an extra inch taken up beneath it. also, i have a 5.2L and i'm on 315 tires. my truck is pretty slow above 2k rpms. any suggestions.. regear my rear diff or what? already have exhaust, so that won't work. how about a chip? thanks.

The rear gear can recompensate the loss you took when you moved up to the bigger tires. The throttle body spacers are said to be dyno proven at around 20hp depending on the application, and it's existing mods. You could do headers, or maybe put it a chip in it, or reprogram the computer what ever it calls for. Those are the cheaper thing anyway. Also look for more improved intakes or cold air intakes.
Jake