I saw a project, years ago, that was losing the "electo-juice" quickly when injector duration went high. It had low-ohm injectors in a system wired without a ballast resistor. it was surely odd, and acted like you describe...running good for 5-10 seconds and then sinking like a rock.
Just one of those simple mistakes, while doing really nice quality work on all the wiring.
Back when I was involved with our turbo car, the outfit that did our computer told us to run a Honda Mini-Trail 6v battery in series before the ignition coil. We weren't spending enough time at low rpm for the 18 volt power to damage the coils (dwell event time gets really short at higher revs). They told us, this was how the Menard V6 Buicks were set up for Indy racing. I was shown one of those Indy cars and, sure enough, there was that Mini-Trail battery in the right side pod!
Everything I ever ran at Bonneville has been battery only. I don't trust alternators in that environment. Plenty of battery is straight-forward easy to manage. Alternators that get kinky in the salt....