charging question

i am having an intersting thing happen to me when i drive my truck. if the a/c is off and the lights are off, the voltage reads right at 14 volts. if i turn my a/c and lights on it drops. sometimes almost to 11.5 volts. i have had my alternator and battery checked at a local autozone. they both passed. i have cleaned the terminals off of the battery. the positive side was pretty bad. i will probably have to replace the cables. the truck is a 95 k1500 with a 5.7 liter. anybody know what it could be? the guy at autozone said that the alternator could be about to go. could it just be my terminals?

Are those voltage readings you listed taken at the battery? If not then I would see what you get at the battery. The gauge in your truck dash is not to be trusted.

Are those voltage readings you listed taken at the battery? If not then I would see what you get at the battery. The gauge in your truck dash is not to be trusted.

Check and clean the ground from the battery to the body.