We're heading back to the states on a Tuesday (probably not the busiest of travel days). Sounds like I should plan on leaving Negril about 3.5 hours before departure. That will get us to Sangster roughly 2 hours before our flight. I think I'll go ahead and book a Club Mobay departure, if they still have openings, just for peace of mind (and we can grab some eats before boarding the plane).
Our original itinerary had our return flight departing at 1:00pm, with a relatively short layover at DFW. Shortly after I booked though, American Airlines decided to cancel that flight and put us on an earlier one (I think it's right around 10:00am). Now we'll have to kind of scramble in the morning, and our layover in DFW will be about three hours longer. :-( Oh well, I'll be well-relaxed after our time in Negril, so it'll all be irie!