2008 6.7 Alternator ?
 

When first starting the truck i noticed that the voltage gauge seems to move up and down like it dose a cycle, dimming headlights , around 30 seconds later after this happens about 4-5 times things seem normal and the gauge reads charging 14+ volts . Didnt know if this was normal for the alternator to cycle when first started or if this is a sign of trouble

The fluctuation you are seeing is your grid heater cycling. You will notice it more when the truck is cold. It's perfectly normal.