Albert,

Hello! I haven't noticed any posts from you in a while. I hope you and your family are doing well.

I've said many times before that it is really difficult to diagnose noises, vibrations and the like over the internet. That said, it is hard to imagine what might be "loading" the engine intermittently, ESPECIALLY a load that could be felt in spite of the massive amount of reserve power that your engine provides.

I am wondering if maybe you got a bad tank of gas and have plugged up the fuel filter. Even if it was changed recently it could be stopped up.

It would be really informative if you could rig a fuel pressure gauge such that you could read it while driving to see if you can eliminate the fuel system or not.

Also, I wonder if you might have an intermittent coil pack or something.

I'm sorry I can't be more helpful.

Take care and keep in touch,