Ok so i'm pretty sure the more people i talk to and the more i really think about it that i have a vacuum leak somewhere..I hear that poor mileage can come form a vacuum leak..When i first but in my vacuum gauge i had 21.5 vacum..And on my way home yesterday idling in my driveway i had 18..I sprayed starting fluid all under my hood and found no idle pick up...How do i go about finding a vacuum leak???Also as soon as i start my truck should i have maxium vacuum or will it take 5 or 10 minutes..Any help would be greatly appreciated..

Thanks