Gas odor when starting 2000 Suburban

Occasionally after starting our 2000 Suburban a very strong odor of gasoline is present and sometimes stays for several minutes while driving. It may last a day or so or go away if you turn off car for a while. A few mechanics don't seem to have an answer. Has anyone had the same or a similar experiance?

has it been tuned-up and serviced , was the de-frost on ??