I think its pretty much one of the only things you can do for your truck next,, seeing as how you mostly got everything else done....I personally would ho with long tubes and generally the long tubes are better than shorties but right now the only one who makes long tubes for these trucks is ARH and their a little pricey about 1600 for the long tubes with cats and y. Pipe so atleast if you did do them you would not be having to get the magnaflow y pipe and you would also be getting high flow cats in the deal....Also i dont even know if they work on a 4x4 havnt heard much about those headers
In the mean time if that seems like to much cost maybe you can sell your 85mm tb and get a 87mm which may help a little bit especially sine you got all the supporting mods, also if you are running the diablo canned tunes i would give hemifever a call to write you a custom tune. I know his tunes have been proven to make more power than the canned diablo tunes