Hi John, As per checking, this is a guaranteed fit for your 2002 GMC Sierra 1500 Base 6 Cyl 4.3L, front direct fit catalytic converter. You can always double check fitment by following the steps below. On the homepage, please enter your application, simply select your vehicle’s year, make, model, sub-model, and engine size and click “Go.” Once your application is selected, type the name of the part you need on the top search box(type "catalytic converter") and press enter. Once the part shows up on your screen, you’ll see a “Guaranteed to Fit, Direct fit” note/badge(in round green icon with a white check mark) if the part will fit, and we recommend that you also double-check your vehicle fit details as well as the vehicle fitment information table on the product page.