Without more data the diagnosis is going to be difficult. Air flow is the first suspect, between both the intake tract and exhaust system. Fuel flow is another question, but inadequate fuel flow or pressure would likely have set a DTC and probably several due to the resultant lean condition. Weak ignition is another suspect, but it is very likely that a DTC would have been set for misfires and cat converter performance.
It would be good to connect a scanner and read the stored AND pending error codes.