I really should take the words of advice at 19A: Reprimand to the overly speedy (ITSNOTARACE) more to heart in my solving experience. I get very easily frustrated when an area refuses to fall into place.
In fact, today, I solved the upper and central portion in under a third of my total solving time, and the remaining section in the lower area took the remainder. A few errors made life difficult for me. I entered an A for the last O in DIADELOSMUERTOS. I've never taken Spanish, but my knowledge of other Romance languages should have made it clear that that couldn't be possible. But to be honest, these were the kinds of mistakes I routinely made on French tests, so it was in good keeping with my nature.
Two other incorrect entries made the SW corner nigh impossible. I put RoutE in place at 45D: R, in a postal abbreviation (RHODE), those two correct letters making it difficult to give it up. And I put in aleS for KEGS.
Eventually, I did what you should always do: remove all and look at it afresh. I was sure that MATHLETES was correct (nice QMC there), because IDONTGETIT was definitely right, as was DOH. Odd to have that and DUH in the same puzzle. Then when I managed CHECKPLEASE, it all came together.
Also great were some of the small bits. I liked 46A: Red states, once (USSR) crossing 47D: Makes red in the face? (SLAPS). Also, 9D: Bring into existence (ERECT) and 10D: Brought into existence (SIRED). That shows an attention to detail, having these related clues so close to each other.
Finally, I'll note the insane 31D: Shortened again (OER). That is such a great bit of misdirection.
Not a race. Right. ROGERTHAT.