Intermittent missfire at low RPMS

[AlphaZulu]

Hello all, I bought a 2017 Tahoe SSV recently with the 5.3L L83 engine. While towing a few months ago I began to get significant misfires and a P0303 code, but only when under load at less than 2,250 RPM. After finishing that trip by keeping the RPMs higher, I changed the oil and on my next trip I got misfires and a P0307 code consistently when under load at below 2,250 RPM.

What would you consider a good starting point for diagnostic? The vehicle has about 91k miles and had the transmission rebuilt at 53k.

Thank you for any assistance.

 

[AlphaZulu]

I guess since no one has any insights I'll just do plugs and wires and see if that helps. I was hoping to avoid the mindless loading of the parts canon, but 91k is probably fairly reasonable for the plugs and wires anyways.