I've not gone through DFW to CZM, but I have through HOU many times. If the flights are on time 45 minutes should be plenty of time.I think DFW only has one flight to Cozumel the 1220 arriving CZM 1500. I only have 45 minutes for me and my bag to make the connection in about 6 weeks.
If one misses the connection is there an alternative?
How about figure out how to get your checked bag back, recheck and get a flight to Cancun and do the bag drag?