1) Yes, you could have a poorly calibrated thermometer and mashed at higher temps, which would've created more unfermentable sugars in your wort.
2) How much attention did you pay to aerating your wort and adding yeast nutrient? Since you didn't post about those steps, we don't know if your yeast just ran out of gas too soon.
What I might try to correct it:
A) Try a new thermometer and mash in at 155 while maintaining a temp of 145 and extend the mash time. If your equipment is erring on the side of running too hot, this gives you a little extra wiggle room to play with.
B) Add an extra 1/2 teaspoon of yeast nutrient to your wort and aerate the heck out of the wort when you put it into your primary. If you use a bucket for your primary like I do, place your thumb over the airlock/blow off hole, tilt the bucket at a 45 degree angle and rock it for a good solid five minutes.