You may also find that while he likes to down from a sit, he's completely baffled by the sit cue from a down position. "Sit" doesn't just mean sitting from a stand, just as "down" doesn't just mean laying down from a sit. If you train the stand position you can randomly move between all three, which makes anticipating more difficult, and at first you may need to go back to luring for a bit.
In Halo's Puppy 2 class we trained sit/down/sit/stand/down/stand, so the puppies had to learn each position from each other position. On the last day of class we had to demonstrate that we could do the complete sequence with just verbal cues and with just hand signals. It's easiest to train with hand signals first, since the lure motion can be faded to a hand signal (no food in the hand), and then once that's solid you would add the verbal cue just before the hand signal. Don't do them at the same time, wait a beat or two after saying the word before using the hand signal - you want him to learn to associate the two, so he needs some time to process the word or he'll just tune it out in favor of the hand signal that he already knows.