As has been stated before - it sounds like your oven thermostate is way out of calibration - especially since it consistently cooks too slow. You need an oven thermometer - one that will monitor the thep of the oven, not the probes that you use to monitor the temp of the food you are cooking.
I would suggest the Taylor #5921N Commercial Oven Guide thermometer
. It's the most accurate and doesn't ever need to be calibrated - unlike the "dial" type that use a metal spring that will get off with time and useage. They will run you about $15 no matter where you get them ... for Sur La Tab to Ace Hardware to Target. The above link was to Amazon just because they have the best picture - and you can enlarge it. Since you have an Ace Hardware there in Key West I would try them first.
As for checking the calibration of "cooking" thermometers ... some can be calibrated and some can't. Dial types that can be calibrated should be set for the boiling point of water - since Key West, FL is at sea level that would be 212°F. Digital models will usually have two calibrations ... a zero or set point (set to 32°F) and a span which is set to the local boiling point of water, again 212°F in your area. If your thermometer is a wet bulb type - it doesn't need recalibration.
CHECKING YOUR OVEN:
Get a sheet of paper and down the left side make a column ranging from 200°F to 550°F (or whatever you higest oven temp is) in 25° increments. This isn't quick but it will give you an idea of what you are working with.
Place the top oven rack in the center position of the oven and put the oven thermometer in the middle of the rack (this should be the middle of the oven) - and preheat to 200°F, wait for 5 minutes after the oven indicator says it is at temp. Pull the thermometer out, check the temp, put it back in the oven, and record this next to 200° , ie, 200° = 135°. Bump the temp up 25° (to 225°) and repeat. Keep repeating this process until you reach the top end of your oven temp range. When you are done you will have a chart of the actual oven temps you get from the dial settings.