Problem with car!! need help

well i have a 95 eclipse gst and just got a 1g swap with an evoIII16g turbo and it was running fine the first couple days but on the third day the car started sputtering. from 0-40-45 it was fine but when you went higher than that or run on 4th or 5th gear you start hearing a sputtering noise out the exhaust and if you down shift and go back to 5th, its fine for a while. now could this be because my car isnt tuned yet. i dont have my safc, fuel pump or injectors yet and wont have them for another couple of weeks. can someone help me with this? and my air/fuel gauge is maxed on richness.

Also what size injectors would you recommend me getting with my setup. 550's? or higher? im not planning on boosting anything higher than 18.

550s for 18 psi should do. Are you flooring it when you go past 45? stock fuel pump could very well be crapping out.

no im keep my foot on the gas at a constant speed and then it will start sputtering so i put it into a different gear and it sometimes comes back sometimes doesnt. actually i should rephrase what i wrote above. ITS WHEN IM OVER 55MPH.