mhansen...
Are you getting your reading from the "tank Monitoring Guages"? I believe they are the same as ours...which reads in 1/3 increments. From what I understand.. when you have less than 2/3 tank... then it will show 1/3 tank...which means 1/3 tank can be anywhere from 1/3 to just under 2/3 of a tankful. Also... your tank is 55 BUT that actually means 44 because the propane tanks have usage of 80% capacity due to safety shutoff regulations.
The important thing is to watch the read out and pay attention to when it goes off of the 1/3 mark. You will still have plenty of propane left at that point to get it filled(roughly 12-14 gallons when it just goes off of the 1/3 mark and is reading "empty")
I hope this make sense to you...
MM