I have a 2000 gmc sonoma sls ext cab 4.3L and i just got put in a 40 series flowmaster with 2.5 inch tail pipe, and runs better more responsive goes good with a stock air box mod with a K&N air filter anyways, the muffler shop doest put any heat shields whenever they put mufflers, and looks like they would if they had any issues by not doing so, so my question is is it really necassary cause i notice that when they gave me a flowmaster stickers in a plastic pouch theres was a notice from flowmaster saying something about make sure before installing your new muffler to use the stock heat shield that came with yor stock muffler.