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Muffler delete

I wouldn't know. I chopped mine off the 3rd day I owned it.
My average is just over 15mpg with the 6.2/10 speed per the cluster. My highest for a tank was 19.7 on a 2 lane road trip with the cruise at 63mph.
5.3 stock exhaust.
My dash info center still shows my best mpg as 22 which is the day I picked it up in Long Beach and drove 100 miles home on flat ground at 65mph to San Diego.
I’ve since added bigger tires and my 40mi round trip commute to work starts at 1000ft then down to sea level then to about 750ft then back home to 1000ft. I rarely get above 70mph. I’d guess I avg 16-17mpg which is pretty damn good for a V8 truck with big tires.
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So, I want to do the muffler/flap valve delete to a Vibrant 3" in/out muffler, but here's the issue that's holding me back;

Ever since I got into cars, I first started learning how people from my dads' car group would modify Chevy 350's. From stock block with decked heads to raise compression, to higher compression pistons, to head pocket porting jobs, and how to clearance a block for a larger stroke crank, etc. Depending on the desired outcome, they'd take a certain path on the build.

This get's me to the exhaust backpressure. The flapper valve is in part to restrict sound and exhaust from escaping. At the same time it creates more back pressure in the exhaust. So if you ask anyone who builds engines professionally that knows HOW they work, they'll tell you, the second you open the exhaust valve, you're letting precious torque out the window.

That being said, for better MPG at low RPM in a high gear, you want torque more than horsepower. This way the engine wont buck under light load or need to downshift. So, if I open up the exhaust, I may notice more downshifts to comp for the loss of exhaust backpressure, resulting in decreased fuel economy on long road trips.

If anyone has already went straight pipe or muffler system minus the flapper valve, please let me know if you're fuel economy stayed the same.
I did muffler delete but kept the flapper valve. Mpg’s have gone up some and still does not downshift when pulling hills that u would think it needed to when the cruise is set. I haven’t owned a gasser in a long time and I’m still impressed with this truck
Maybe with a old carbureted, no electronics, open headers engine, you would need some back pressure.
A modern ECU controlled engine with a full exhaust including catalytic converters can compensate for the loss of the muffler and probably benefit from it.
I'm gonna say NO to loss of torque. I dynoed mine with just the muffler/flapper delete. 387 HP 465 LB/FT Torque on a 90+ degree day with 60% humidity. It's only rated at 460 LB/FT of torque at the flywheel!

Just muffler delete. I chopped it off 3 days after I owned it so no chance to dyno stock as this was at the dealer's car show they do once a year in August.
Since I did the muffler delete, I can definitely tell the difference between L9 and Drive. L9 all the gears go up and down as they should. Drive u can hear when cylinders shut down and when they kick in. L9 is all I do now

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