Engine stutters when accelerating after warming up

I've been having this issue for a bit and I don't want to start changing unnecessary parts. My vehicle started with this issue where it would start to stutter, lose power and hesitate once it's warmed up. Oddly enough I've noticed when the engine is cold, the stereo starts to cut out when I'm accelerating and then it starts hesitate when the engine is warm and the stereo is normal. A while back my mechanic changed out an ignition coil cause when I first started with this issue, it was throwing out a misfire in the first cylinder but he mentioned a misfire in all cylinders did pop up which was weird but he thought it may have been cause of the first cylinder misfiring so he told me to try driving for a few weeks and see if that corrected the problem. Spark plugs are brand new and I'm not getting any check engine lights as of right now. Would also like to add that I took it to an AutoZone and they checked the battery and alternator for me and the battery tested fine but when he went to check the alternator, it said that the battery didn't have enough of power to accurately test the alternator. I'm leaning towards some sort of an electrical issue but I have no idea where to start.