performance intake

So as i know a 2011-2012 mustang comes stock with 305hp and approxiametly 31 mpg. I have done my research and so far have learned that it has a bit more hp than that and a little under 30 mpg highway. I was just wondering what you guys thought i could get out of it with aftermarket parts, such...

i have an 88 gt 5 speed and just put on tf street heat upper and lower, bbk 70 mm tb w 70 mm egr and bb fenderwell cai..now when i push on the gas it wants to miss a lil but then drives fine until i shift and press back on the gas then it does it again..also when i get on it it seems to wanna...