Is a custom tune needed with a pulley swap?
Usually, yes. For an upper pulley swap, with a pulley smaller than 3.2″ you should at the very least get a dyno pull with a wideband A/F check. In general, you want the A/F ratio to be below 12.0 (12 parts air to 1 part fuel). Rule of thumb is that any time you install a motor mod, get your A/F checked.