Need help with DTC P0300, P0301, P0303, P0304

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After several resets by dealer & self and replacing spark plugs (not spark coils) still getting codes. Dealer only seeing misfire codes 1 cyl at a time; I am now getting the multiple random DTC and several individual. Engine very rough on cold starts & throwing misfire codes then. On cleared hot starts is fine until heavy load or high rpm acceleration, sometimes won't shift to 4th. Get 1 sec flash check engine and rough rpm. Since all cyl affected suspect fuel or vac leak. Vehicle has 108,000 miles. Have run fuel inj cleaner in one tank, now running dry-gas in another tank at dealer recommendation. Can't find reliable info on fuel filter replacement. Vacuum leak possible too? Getting no other DTC's. Thoughts?