Low idle Ford Lightning SVT 5.4
 

600 rpm rough idle in drive, 850 in park, no codes at this time, 40-60 mph runs like it has a misfire. lean rich gage eratic at all times. I have checked pcv hoses and fittings: ck good, replaced:fuel filter. Cleaned Air filter. replaced plugs
and cleaned o2 sensors and map sensors. Had a diagnostic ck done a month ago, had misfire at that time, coil was isolator was replaced, and #2 Engine lean code: exhaust gasket replaced. iAny ideas what i need to do to fix this?