Howdy, Pard,
I have zero experience with the NEW Vaqueros, but the Old Models typically ALL shot low at 25 yds because Ruger intentionally left the front sights a bit tall so shooters could file them down to raise the point of aim with their favorite load. Lighter-than-standard bullets will generally print low since the barrel has recoiled (muzzle raised) less when the bullet exits the muzzle.
St. George's point about the gun shooting differently from a seated and sandbagged rest than when shooting one-handed (and standing, at that) is SPOT ON! Try using a rest for your forearm from a standing position, with the gun where you will normally hold it.
Hope this helps.