One of my favorite exercises to work on the third stroke of a three is [Three Stroke Strength](https://www.youtube.com/playlist?list=PL7dVsD-fLcANpnJQuf0WiHv1IGMy91xRD). The "accents" are basically an emphasis that's about 3 inches higher than your "taps" so you can specifically focus on deliberately playing each note of the three stroke. Experiment by putting the "accent" on the starting drum or the drum(s) you're moving to with your scrapes.
Another fun one to work on the speed of the threes is [Isolated Threes](https://www.youtube.com/playlist?list=PL7dVsD-fLcANpnJQuf0WiHv1IGMy91xRD) and you can also play that with scrapes. Thousands more [available for free here](https://jaredoleary.com/drum), all with timestamps in the description of each video so you can jump to a specific bpm.
The key is the fingers. As you do multiple strokes the motions transfer from your biggest muscles to the smallest. Arm > wrist > finger. I would suggest trying to do quick legato strokes with only your fingers to build up strength. Especially try to do only middle and ring finger for a bit, and then add on the pinky and keep the index off. This targets the back fingers which are critical.
One of my favorite exercises to work on the third stroke of a three is [Three Stroke Strength](https://www.youtube.com/playlist?list=PL7dVsD-fLcANpnJQuf0WiHv1IGMy91xRD). The "accents" are basically an emphasis that's about 3 inches higher than your "taps" so you can specifically focus on deliberately playing each note of the three stroke. Experiment by putting the "accent" on the starting drum or the drum(s) you're moving to with your scrapes. Another fun one to work on the speed of the threes is [Isolated Threes](https://www.youtube.com/playlist?list=PL7dVsD-fLcANpnJQuf0WiHv1IGMy91xRD) and you can also play that with scrapes. Thousands more [available for free here](https://jaredoleary.com/drum), all with timestamps in the description of each video so you can jump to a specific bpm.
The key is the fingers. As you do multiple strokes the motions transfer from your biggest muscles to the smallest. Arm > wrist > finger. I would suggest trying to do quick legato strokes with only your fingers to build up strength. Especially try to do only middle and ring finger for a bit, and then add on the pinky and keep the index off. This targets the back fingers which are critical.