Thanks for the insights. I'll catch y'all up on progress.
I'm recent to the game of CNC. My only real-world software familiarity is with V-Carve Pro which decides much of how the spindle will move when choosing the "V Carve" toolpathing. This limits what one can choose in the way of cutting direction which would be available in a different toolpathing option, such as pocket or profile. I suppose it would be possible to cut this as a 3D model, but with a way-too-long process time. While dust collection is good by my standard, I don't currently have ability to shoot a stream of air at cutter...an interesting idea I'd like to hear more about.
I've troubleshot in many of the ways suggested. Spindle speed up to 20,000 and down to 15,000. Movement by increments down to (way slow) 20ipm. Shaken, yanked on, inspected, greased, all I could think of on gantry. Narrower angle V cutter, different tool holder. I suspect the problem is magnified by the shallow angle cutter. I don't really think this is what I term as chatter, which would be more like material hold down problem or spindle/ cutter run-out issues. Perhaps that's my distinction only. It might also be somewhat material related. When I get a chance, I'll run test battery on solid surface material and see where that takes me.
I tried to methodically leave no stone unturned. I was able to reduce size of scalloping cutting in a single pass significantly by slowing down below 60ipm. Near perfect at 20 ipm, but I imagine the cutter churning away in a flurry of MDF swarf, maybe even burnishing the surface. Besides that, it's just too slow for the production I envision. Good surface finish was also achieved by a .005 final pass. Downside is that doubles machining time which shoots foot of production.
On the horn with ShopSabre we discovered a slight, I'm guessing .003-4, in Z ball screw endplay. Shims to bring that closer to 0 on the way. I'll update once installed and tested.
Thanks again for the help with my big toy!