Befor you do anything else... if you haven't already, take your truck out on an open road & run it at 65mph minimum for 20-30 minutes or until message clears.
That would drive me nuts.or else you have to live with the ding ding dinging every minute.
The only way to clear your cat full message is to clear codes on start up everytime or else you have to live with the ding ding dinging every minute.