How long did you cook them for? Also, maybe consider cutting them in half to avoid the issue.
On a different note, make sure your fire isn't running too hot from the get go. Using too much lighter fluid and lighting too many briquettes can make your temps be too high. Try lighting on 10-15 pieces in a chimney and then place them in the center of the basket. Place the basket back into the barrel and with lid on, allow 15 to 20 minutes for the charcoal to settle in and roll sweet blue.
Works perfect for me and I've never had an issue of overcooking anything on it. Hope that helps ya!
18.5" OTS, 22.5" OTG, CB Silver(Rip), Vintage Coleman Bullet, Pit Barrel, UDS