TurboSpeed

Brand new spark plugs, got both the coil-pack rebuild by RMT in FL last year and a year later having P0300 (random) along with Clyinder 1, 5 and 6. These are the only cylinder that are misfiring and it only happens when I accelerate hard or full pedal. I can't believe if i have to send it out again to get it rebuild. Is their anything else I can check that might be causing it, its odd it only happens hard acceleration and its always random but sometimes all 1,5,6 show up, sometimes only cylinder 5 shows up. I can drive the car normal with out triggering the check engine light but im about sell the car and want to get this addressed before selling.

Its a 2004 Mercedes s600. Any advise help be great, is their anything else that might be issue here since it only happens at hard acceleration with same cylinders misfiring ?