I want to gut my cats and put true dual dynomax muffs on my 99 5.3, but the gey at the muff shop said that i would have problems b/c it would my backpressure to low and it would not run right. Is this true?

 

absolutely not, in my experiance, and i believe everyone here on this board will back me up, is that lsx motors do not need a ton of backpressure, like some of your run of the mill, older style small block chev's. Open that baby up, and you'll be happy.

 

is ur truck stock? if so, backpressure would make a difference. without enough of it, your initial torque off of the line is greatly damped. Atleast I noticed this big time on mine with true duals, being almost completly stock, (just an intake). but... ur in upper rpms, ur motor will flow alot better which will give u a little better pull. my 2 cents