Stock muffler and tailpipe
 

i got true duals with 18 inch glasspacks now, with 2 inch pipe and no convertors, keep in mind this is a 4x4 do the pipes are right beside each other, if i were to have the glasspacks cut off and put a y pipe on and have a single factory style replacement muffler and a 2 1/4 or 2.5 inch tailpipe, how much power and mpg should i expect to loose?