Without any codes,it can be tough to diagnose sometimes,especially with COP (coil over plug).....
A misfire under a load is indicative of a secondary Ignition breakdown ,I.E. ,coil(s),Spark plug(s),Wire(S)...Etc and/or a LEAN misfire due to low Fuel Pressure.
Has anyone monitored the Fuel Pressure while the symptoms/concern is present?
Replacing all coils can be expensive ,if you have the time yourself,purchase one new one and install it on number 1 cylinder and road test it,no change,move it to number 2,etc....Tedious and time consuming but may yield results.
Recommend a new set of spark plugs as well while doing this,
Any parts replaced ? Reason i ask,is aftermarket coils are known not to function well on this engine.Stay with OEM coils.