I didn't see where anyone mentioned opening the filler cap when the engine begins to sputter. So, I'll mention it. When you open the cap (slowly) you should here a gentle "whooshing" sound if there is a partial vacuum in the tank. That could confirm an EVAP problem if there is one.
Just filling in a minor blank left by the other and excellent recommendations.
-Sticks and stones, love.
-Insurmountable problems exist in the imaginations of the less traveled.
2011 BMW R1200GS, 2004 KTM 950, 1996 ATK 605 ESDS