Evderyone I have heard has said that the non ethanol fuel does infact get better gas mileage. However where I am at I can not find the non ethanol fuel. Where are you seeing it?
As far as the exhaust I bet it is stock. Maybe it was welded back on, but definately stock. Got any pics?

 

no pics but i can take some tommorrow ill probably be putting in my cb tommorrow so i can snap a few pictures of my exaust while I'm out messing with the truck.

the availability of non ethanol fuel sees to vary greatly depending on where your at here the majority of stations have non ethanol 87 oct fuel. just fueled up today came out to 9.7mpg about 90% city driving on 89oct 10% ethanol fuel. when driving by fuel stations if the low and mid octane fuel are the same price both are probably 10% ethanol if the 87 is higher a higher price its probably non ethanol fuel and look at the stickers on the pump (not all fuel stations have the stickers showing that there fuel has ethanol in it though) when i fueled up today the non ethanol 87 octane was 6cents more per gallon than the 89oct 10% fuel

 

here are some pictures of the exaust, it was starting to get dark on me so i couldent get very good pictures, also laying on my back under the truck does not make for good picture taking...lol

this is a picture of where the exaust is welded on just past the manifold, both sides look the same only took a picture of the drivers side



two separate pipes from both manifolds that do not connect until the muffler.




one catalytic converter for each pipe they are offset you can only see one of them in this picture. you can also see where the two pipes go into the muffler


here is a picture of the muffler


single outlet from the muffler


this is on a 8.1L 496 3 inch pipe from the manifolds to the tail pipe, not sure if it is stock or not maybe you guys could tell me, looks like it would be stupid easy to dual out. don't want loud but a little grumble would be nice.

 

Yeah it looks stock to me. Looks like my cousins 6 liter. I would cut out the stock muffler out and replace it with 2 mufflers (your chioce) side by side and dualed out either out the rear somehow or possibly dump it past the axle.
Normal Mufflers that I see on the forum:
Flowmaster - 40 series, super 40s, super 44's, 50 series
Magnaflow - 14 to 19 inch case
Glasspacks
Spintechs - I think they are called.
I run a Flowster clone and I like the sound and performance out of it.
Anyhow thats what I would do to dual it out. Just mufflers and tailpipes will get you a good price versus a catback system and possibly the sound you want.
Does that muffler actually exit out the rear dualed and then into a sinlge tailpipe? If it does you can cut the single tailpipe off and run it dualed that away. I asl if the muffler is that way, because my parents Avalanche is like that and my friends Denalli is too. On the Denalli we cut off the tailpipe where it went exits as a dual and goes into the single tailpipe and run the duals. The denalli ran better, but the Flowmasters we installed later as a dual set up was a much better improvement. The Flows where welded side by side.

 

This dealership is saying they have a 2003 4.8L V8 AWD. I didnt think they made 4.8L in 2003 but anyway its probly gonna get around 15mpg since its awd right? I am just looking for atleast 20 mpg. if this info helps you guys answer my question.