Truck runs fine and then I stop it revs getting out 1st. Turn truck offon it runs just fine.

Question

I have a 99 Silverado, I can start the truck up fine and drive . It shifts through all the gears. Then out of the blue, mainly after I come to a stop and then I go, it revs throught 1st gear and then it sort of revs into 2nd, but is fine after that. If I turn the truck off, let it sit for a minute then back on it's fine and I can continue to drive without it reving throught gears. The check engine light has come on a few times, but always goes away. I don't want to take it to the mechanic shop and pay for a diagnostic if the problem needs to be addressed by a transmission shop. Anyone have this problem or know what the cause is and which shop I should take it too?