Thanks, Mike. Haven't tried a capo yet, but it does sound like a good idea and I'll pick one up. I definitely have an easier time with the shuffle when I move it up the neck and can play it in a different key.

The thumb point is painfully obvious to me already! I move my thumb more into the middle of my hand, say around fret 4, when doing that part of the shuffle otherwise I can't make the stretch at all. I'm not fast enough yet to make this move as quickly and smoothly as I need to, and I'd rather not keep it there all the time when playing the E and A part of the shuffle. So I still have some work to do. However, I'm pretty happy that I've made it this far. I can also tell a real difference between the frets on my Epiphone Dot (easier) and on my Martin acoustic (a bit harder) which I guess are using a slightly different length fretboard.