when i start my truck in the morning the volt gauge on the dash shows about 10-11. the check gauges light is on and then after about 30 seconds it shuts off. i replaced the batteries a few months ago and im worried the alternator isnt working right. does anyone have any ideas?

Test the charging voltage at the batteries after it is warm and the grid heaters are not working. When you first start the grid heaters are drawing 200 amp, you have just drawn 200 amps for the pre start so the alternator has to charge a bit till the voltage rises enough for the check guages light to go out. Basicly normal. Time your check guages with a watch to see how long it really is on. The colder the ambient temperature the longer the light stays on.

Test the charging voltage at the batteries after it is warm and the grid heaters are not working. When you first start the grid heaters are drawing 200 amp, you have just drawn 200 amps for the pre start so the alternator has to charge a bit till the voltage rises enough for the check guages light to go out. Basicly normal. Time your check guages with a watch to see how long it really is on. The colder the ambient temperature the longer the light stays on.

Probably only your Grid heaters working at start up.[coffee]