[spdbrake]

Meant to ask you when you say "breaking up" @ 5800, you were on a dyno correct? If so the operator most likely/ should have had a O2 sensor on one of your sidepipes. I'd ask him what the AFR changed to at that moment just prior and then @ the breakup. If it leaned out I'd start looking at your fuel supply (Old hoses, filters and the like). Ethanol is not kind to rubber.