+1 Man

So do I, one muffler no cats as posted. Lots of people here run this way and most never complain about losing power like you are.

 

i run stock manifolds, jegs y-pipe. no cat. both o2 sensors where they're supposed to be. a big single in/dual out muffler, dual exhaust out the rear.

no cel and its relatively quiet.
i prefer the pipes out the rear so you don't hear the exhaust reflecting off everything you pass by.

i bought the y-pipe for about $150 and spent $250 on the muffler/installed and remaining pipes. you can sell your stock cat for $75 on the internet. that helps a lot.

 

What's better efficiency (i.e., power, fuel economy): Duals that begin at the manifold or a single pipe to the converter and then duals?

 

Lol at that.

A single pipe off each manifold is best, then just keep going out the back of the truck, so a full dual setup.

 

Had to reply to this, just thought it was funny you are looking for fuel efficientcy. If this is true you are deffinatly driving the wrong vehicle.

 

Now THAT is an accurate statement.

(and: welcome to DF! )