I've got a 1976 Chevy Cheyenne with a 350 on propane.  I currently have dual 2 1/4" exaust with glass packs, it's way to loud and I need a change.  I'm looking for a quieter muffler, that doesn't take away my good mileage - something similar to the flowmaster design but more cost effective.

Any suggestions?  I need some help!  

i've got a suggestion... get rid of the dual exhaust... you'll get more performance with a y-pipe to a single in dual out muffler... then you only have to buy one muffler instead of two... and it'll sound better too... it'll have less "pop pop" and more grumble...  and cherry bomb makes a new muffler that isn't a glaspack... if you pay attention to the hot rods and what not... they all go to an x-pipe then back out to dual exhaust...  it helps with easing valve operation or something like that... i don't remember exactly...