My question is if there is any way to tell how much DEF is in the tank. I have had the truck just about a year, in August I did need to put some in, the message center said it was getting low. I was doing to towing on vacation pulling my fifth wheel trailer. I know that when the truck works harder the more DEF is used. Since that time I have not put any in the tank, the system says level is OK. I have probably driven 6,000 miles since then and no messages that more DEF is needed. I guess I can just trust the system, but I am curious about the amount being used. I will be heading out for a long trip in another 6 weeks, I just don't want there to be any problems. Suggestions? or am I just worried over nothing?