for the comment about operators not allowing OW divers to do drift dives. This may be applicable in some places but not Cozumel since most, if not all, the dives in Coz are drift dives. I actually did my open water check-out dives in Cozumel, from a boat, so I started out drift diving. And then I was hooked!
I also have to comment that you don't necessarily lose your group if you can't get down right away. I have difficulty equalizing due to scar tissue in my eustachian tubes, and so I generally take longer to descend. I inform the DM as we're riding out to the site to let him know of my problem, I take my time and drift above the group, with the DM keeping an eye on me, until I can get down. I have dove in Coz 6 times (and counting--17 more days to my Thanksgiving trip!) and have never lost my group as a result of my inability to descend quickly.
Drift diving can take some getting used to though--your inclination will be to kick too much and use your arms to keep your balance. You'll probably start out trying to fight the current, to maintain some sort of control. Don't do ANY of this! As soon as you hit the water, get yourself ready, take a deep breath and start your descent when the DM signals everyone. Focus on breathing normally, relax and try to move your body as little as possible. If you kick and the current is strong, you will end up WAY ahead of your group before you know it. Stay behind the DM during the dive--don't get ahead of the group.
Since you're diving with 2 DM's, you'll be better off than some, but that doesn't mean you're invulnerable. YOU are ultimately responsible for your own safety. Listen closely to the dive briefing, go over emergency procedures especially if you run into a downswell (not common but it can happen and you need to know how to handle it) and watch the other divers and the DM leading the dive. As the others have said, pay close attention to your buoyancy, especially once you get on top of the reef or if you're doing a wall--check your depth gauge often and watch your time. And you will always need to do a safety stop--if you have difficulty hovering at 15 feet, take a safety float or something to help you stay at a consistent depth during the safety stop. Sometimes the DM will have one--ask.
Drift diving can be effortless and very relaxing but don't take it for granted--accidents can always happen but the better prepared you are, the better you'll be able to handle whatever happens. You are going to love drift diving and the clear, warm blue water--have a great time!