Right now I've got a Flowmaster 40 Series Delta flow on my X and I want something a little louder so I want to move up to the regular 40 series. I also want to run dual pipes since I've got the spare tire out of the way (Shrockworks rear bumper should be here in a week! ). I was looking at the flowmaster website and the only dual out 40 series they offer is 3" in and 2.5" out. I know the 2.5" out will work but I wasn't sure about the 3" in since stock piping is 2.25". Can they like put an adapter on there so it'll fit?

Yes, they can put an adapter in to make it fit.

One last question. Should I do 2.5" from the muffler back or 2.25"? 2.5" would obviously be simpler and cheaper but would I lose too much backpressure?

anybody???

If you want something louder, I wouldnt go original 40 series. I have it on my truck with 2.5 out the back and its not loud enough for ME. If I were to do it again I would go glasspack...just my opinion...