Yeah maybe a hair larger but its still considered a 2.5". If he is looking to replace just the muffler he wants a 2.5 inch offset in center out (make sure you have it welded in).
My friend has the MBRP 3 inch exhaust on his 06 5.7 liter Commander. It sounded like crap so he swapped out mufflers with a stainless steel flowmater 2 chamber muffler (Cant remember off hand which series). It's sounds amazing now.