Noticed this lately, especially if truck sits for a full day and/or when it is below freezing out. Voltage dial on dash drops from around 14 to 11-12 along with dimming headlights, slower fan motor, etc, anything electrical "slows down" when the voltage drops. Then it will pop back up to 14 and everything will be fine, repeat that process for about 10-15 minutes and everything returns to normal. Should I have the alternator tested? The battery is only a year old, DieHard Gold with 700CCA.