You're thinking of (planeside) valet checking, or at least that's what DL usually calls it. Gate checking is the term that DL applies to bags that won't fit in the overheads (because they're full, not because they're too big), and they are checked through to baggage claim at the final destination. If the bag is roughly carry-on size, you might be able to get away with it, but TSA has been known to turn people with steamer trunks around to check them properly.