Mysterious Misfire(s) codes 2.5 gt

[lee07]

Please help me find out why why check engine light is one. I have a check engine light for misfire or misfires.Now it will flash 4-5 times when driving. Sometimes its one misfire code sometimes misfire in 2 or 3 even all four misfire codes. I changed one fuel injector, one new ignition coil, also swapped them around ,new spark plugs denso irrdiums pre- gapped new front o2 sensor. Had 5 repairs shops look at it none of them know what it causing a misfire. Compression one shop was around 140 another said was good another said was low 15 psi. car use to have a erratic idle hunting 100rpm-2000rpm. Now idles fine at 750-800rpm no hunting anymore.Car runs ok. Still can get up and go but maybe 25% power loss. Car doesn't eat any coolant or oil. Smells and looks like normal.NO excessive white smoke from tailpipe. Tried the dollar bill burned exhaust valve test. It didn't suck the dollar in.No loud noise or tapping from engine. but does shake quite a bit sometimes will feel it in the car.Car also has a hard time starting sometimes only like once a month. Had A Subaru check for bad Head Gasket they said was fine. Check and sprayed for vacuum leaks, cleaned throttle body and MAF SENSOR. Doesn't over heat. PLEASE HELP TELL ME WHATS WRONG. COULD IT BE A BAD cat was thinking maybe was clogged cat or fuel filter? Been hunting this since October