You can get a custom cut 05+ grill that has been trimmed to fit 99-early03 trucks. its $325 on ebay. You can get the billet grill, but you have to cut up your stock grill, i dont personally think it looks very good... that 05+ one makes a big difference.
If you cut the grill yourself, you will have to zip-tie it on, if you get the one off ebay it will go on factoy hangers....i think thats what it says.
I have a 5" turbo back exhaust with a flow through muffler ad 4" down pipe from farmboy diesel-----about $400
cat back doess not sound much different than stock...and would not really help with flow. I would get that farmboy exhaust or get some Aussie cut stacks!!!