I have a 04 Silverado and for the past couple of days I've been having issues with putting gas in my truck. Once the pumps start it will only pump maybe 1 gallon then it thel automatic shut off kicks in. It's been taking me 5 mins to put 3 gallons in. I've checked to see if there were any leaks in the tank but I couldn't find any. What could cause this and would this be an easy fix or and expensive fix? Please help!!