My 5.0 has 76mm maf, 70mm throttle body, 24lb injectors, headers, cold air kit, and underdrive pullys.  when the engine gets warm(mid way on temp gauge) the check engine light comes on and she loses power while spitting and sputtering at me.  after i get up to speed she smoothes out.  had the code read and replaced o2 sensor.  still doing it.  any help???  

Sounds like the MAF has gone bad. Try swapping out and see what happens.  

Hi im sean frome south ga. nice to meet you all i have a wrecked 88 mustang 5.0 HO (x gsp car)and a 93 mustang whith a 4 cyl. how hard is it to change the computer and harness?