Mash temperature question

I recently did two similar all Brian brews both used so4 yeast. Both were about 1.050 initial gravity. I mashed both pretty close to 154 for an hour with a no sparge technique collecting all running a into the kettle for a 7 gallon boil for 60 mins each. My question is in regards to their finishing gravity. Both beers finished quickly. The second one went from 1.048 to 1.020 in 36 hours. Both were repitched slurry from a previous esb brew. I actually repitched on the second one thinking I could get the fg down to 1.010 or so where I wanted it. After a couple weeks it was still at 1.020. The other beer started at 1.050 and finished at 1.018. I am wondering if something is wrong with my thermometer and if I am seeing the results of a higher mash temp. Both seem fairly dry and not big in mouthfeel but the fg has me worried. I would have thought s04 would attenuate down a bit lower than this. I had the same finishing gravity. 1.017 on the brew I repitched the yeast from...it started out in the 1.070 range with two packs of s04. Thoughts on how if this should be corrected?

Thoughts:

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.

Sorry need to clarify. I did aerate with a drill and wine degas wand for 60 seconds each. I added a tsp of yeast nutrient to the boil. 64 deg for whole ferm cycle 2 weeks.

Both these beers ended up carbing up fine in the keg after a couple weeks. They ended up tasting great even though they finished high. The sweetness that I noticed before on the bitter has subsided with time and has been offset somewhat by the dry hopping I am doing in the keg. Neither beer is stellar but both a good and drinkable. Thanks for the response. I am thinking this is standard behavior for SA04 with my setup. Checked thermometer in cold ice water and it was right on.