I checked the wires for breakage, re-tightened the connectors, and tuned on the Mach3 motor screen for hours; and it would STILL randomly stall-out!
Thanks for the advice, everyone, but I've given it up as a bad job!
Gone and ordered a ShopBot Buddy.
It'll have the flexibility to cut large and small projects in a small footprint. Also added an Rotory Indexer, so I can expand my cutting in a whole new direction! Can't wait!
ShopBot Buddy 48 w/12" Z + 8' Powerstick and Indexer