Ph can do strange things sometimes. The calculators are great but sometimes the actual ph will vary unexpectedly. On my last brew day I calculated acid and salt additions for 5.5 mash and sparge, then a preboil of 5.0 ph. I gathered samples along the way. I did two brews with the same profile. After I was all done I did the lab work. Actual ph was 5.5 mash, 5.7 sparge, 5.0 preboil and 5.0 post boil with beer #1. Beer #2 was the same numbers as #1 except that the post boil ph actually went up to 5.1 ph. To me its odd that the calculations were right for the mash, off for the sparge, but then right again for preboil.
Back to your beer. 5.5 target and 152F seems in the ball park but that ph is kind of right on the line between top end for beta and sweet spot for alpha. 152 is getting to the top end of beta sweet spot and bottom end of alpha sweet spot. So a slight ph drift up would easily explain that 4-6 points extra FG. especially if it doesnt "taste" sweet. Dextrins reportedly dont taste as sweet as maltose. Sounds like yeast did its job, you just got a little more dextrinous wort than you expected.