Primary Ignition: Does your tach jump wildly + or - approx. 1000rpms when you have the missing/stumbling issue? If yes, then you have an issue with your primary ignition components
Secondary Ignition: Does your tach jump wildly + or - approx. 200rpms when you have the missing/stumbling issue? If yes, then you have an issue with your secondary ignition components.
The Primary Ignition Side:
The best way to define the primary components is that they are the parts that deal with the low voltage from the battery (the 12-volt side). Note that all of these parts use conventional wiring since they’re carrying lower voltages (except the battery cables that connect to the starter and alternator). This includes the battery itself, the ignition switch, a switching device, and the wiring that connects to the coil’s negative and positive terminals. The coil works on both sides of the fence since it is the point where the primary and secondary systems meet as it takes a high voltage in but sends out a high voltage spark.
The Secondary Ignition Side:
The spark plug wire that connects the coil to the center terminal of the distributor (called the coil wire) is where the secondary side of the ignition begins. In stock systems, there is generally anywhere from 10,000 – 20,000 volts bolting through this wire. This spark zips through the wire and transfers to the rotor tip and then jumps across a small gap to another cap terminal. From there it moves out of the cap, through a spark plug wire, and finally across the spark plug gap. It is important to note that these secondary components, the cap, rotor, and spark plug wires, are maintenance or wear items/parts. Depending on your use, they should be inspected at least once every cruise season and numerous times during a race season
If your Tach doesn't move when you're having this issue then it's either fuel or mechanical failure (engine). Does this issue only happen at WOT? Can you go to 6000rpms at a steady rate? If you can then it's not the MAF meter.
I hope this helps