Toothpick test works great too, as mentioned above. Take a toothpick and poke between 2 bones - it should slide in and out without much resistance.
I spent many cooks foiling and unfoiling and all kinds of permutations of the 3-2-1 method and i got sick of it (besides spending a lot of time and money on foil). My last rack of ribs was a rack of untrimmed spares going at ~300 on my egg, done in a little under 4 hours. Best darn ribs I've ever made, and no fuss.
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