I have an 05 silverado I just purchased. after about 100 miles the engine warning light has come on (not blinking) but steady. I put Mid grade fuel in it about 60 miles ago. I have not driven thru any large puddles, and the fuel cap appears to be on tight? My question is how long does it take for the light to come on if I got bad fuel?? I am consederably concerned since I just bought this truck, but the manual says don't panic until the light is flashing?? Any info would be helpful??