Theres also an easier remedy if your willing to crawl under the truck, look at the inlet side of the muffler and find the part # that is engraved, go on summutracing.com and type it in and see what comes up. Some exhaust shops dont even know the part #s are engraved because its very small and unnoticeable especially on black painted mufflers.

 

That too lol. Or take a picture, chances are, we could eyeball what it is.