Installed PV system questions

I have a 33 panel system with REC 235PE panels. They each have a Tigo monitoring system which is then fed to a SMA 7000 watt inverter.  I have had this system for about 3 years.  My installer bailed on me so I have been working on the system myself.  I have had a few modules go out but Tigo has been good about sending me replacements.  Anyhow every year my annual bill increased from about $100 to $400 and now $800.  I have been putting more thought into this system and notice, per Tigo, my panels don't produce more than 180W peak but more around 160w.  The voltage is about 25 volts per panel.  I contacted REC and they said if i plug into them directly with a meter and they are less then 30volts they would replace them.  They are all doing that so I am thinking it is not the panel.  Tigo said it may be the SMA inverter programing? but I don't see any information on how to program it.  Each panel, per Tigo, is producing around 5 to 6 amps.  3 strings of 11 panels each.  I looked at the wiring to the stings and the installer has 10ga wire.  If that is correct that would be about 55 to 66 amps per string.  It is about 100 feet from the panels to the inverter.  So now is the wire to small?  Is the inverter need to be programed?  Are the panels bad?  I don't know where to start.  I tried using the calculator because I though maybe the wire was choking the system but just adding the amperage and distance doesn't seem like the 10ga is right?  Lastly the system runs at about 260volts DC to the inverter. The panels are facing primarily West. Any help would be appreciated

John