backfiring or ??

My 2003 Victory Classic Cruiser at 3000 RPM's or 70 MPH backfires or stalls out only when I'm riding it, not sitting in the driveway revved at 3000 RPM's. 4 days ago I put in 2 brand new NGKR CPR6EB9 sparkplugs. Symptom went away for one day then came back today on the way home from work. Put new gas in it this morning on the way to work. Same gas that I always use. Any ideas on what could be causing this?

Lots of variables. Easy stuff to chck first.
Remove, and clean battery conections. These things live, and die with battery voltage

Make sure the plug wires firmly click onto the spark plugs

A couple of squirts of brake clean at the throttle body adaptor to check for vacume leak

Fuel pressure should be 49psi at idle, and cruise