Check your "Output Voltage" with: Headlights on high, flashers on, Blower motor on High and the fog lamps on. Should stay above 12.9-V, over 13-V would be best.

Try disconnecting and reconnecting the glow relay to see if there is a significant change in output voltage. 13-V does not seem low enough to raise my eyebrow, assuming the alternator is under an adequate load.