Engine bogs out and has missfire

The flashing Check Engine light means you're supposed to stop the engine as quickly as possible. Too much unburned gas is going into the exhaust system where it will burn in the catalytic converter and overheat it. The place to start is by having the diagnostic fault codes read and recorded. Those will indicate the circuit or system that needs further diagnosis.

The misfire is why there is low power. Since you already have new spark plugs, I'd start by double-checking all the wires are on in the right order. Every professional has made that mistake more than once.