You can always sink a buck or two into those little tension stops to see if that might be the issue. They are round on one side, and flat on the opposite. That flat side keeps the tension rod from moving. You tension it to where you want it and then force the nylon tension stop onto the top of the rod. It forms around the top of the rod and keeps it from turning. It really works. Check it out and see if that helps.

I'll check them out, thanks.

The head isn't seated properly and uneven tension.

Seat the head by pressing in the center of the head just before you tune. Tension rods are loose but not sloppy, just enough to hold head in place while you press. You'll hear cracking and stretching of the mylar and glue.

Finger tighten rods until snug then begin tuning.

Use this chart to tighten your rods, full turns each go around until you have the sound you want.

If it continues to go out of tune, check your rods for stripping/misthreading and swivel nut as well.

You have a tension rod that is loosing up ..

That's what I thought. Tension Stops are the answer here.

YOU SAID RIMSHOTS,I have had that problem with drums that have thinner hoops,usually it will be one -t-rod that is the culprit,the tension stops may help,although one time I had that happen with a 12 tom that i would ride the rim on for a rockabilly tune,later I checked the bearing edge and found a fairly long dip in it,and noticed that whenever the tom went out of tune a little bit just from regular playing it was at the area where the dip was.Might check the edge as long as you are troubleshooting it.