Hiya,
So there's a few options here.
First of all, it is entirely possible he does need a bigger tank. Instead of giving the measurement in gallons, could you give the width/length of the tank? They come in different dimensions and my advice regarding tank size partially hinges on that.
Second of all, what kind of enrichment opportunities are you providing him? Does he have multiple hides and perches? I've found that this can go two ways - My boy Guacemole has gotten "angry" at me for moving his favorite hide and glass surfed until I put it back, and I've also had him glass surf for a few days until I re-did the interior of his enclosure and swapped some of his enrichment items. I also have found that a lot of BD owners don't give their animals suitable hides and that glass surfing behavior often improves when they have 1-2 available. This one might be particularly suspect based off the body of your post.
Third, is there a particular wall of his enclosure that he's surfing on? What kind of enclosure is it? Most beardies to best with 3/4 walls of their enclosure opaque. If you're using an all glass enclosure, you can tape construction paper to the outside to achieve this effect. You also might want to check if he's seeing his own reflection in the glass - many beardies will attack or try to run away from their own reflections, which they perceive as another dragon.
Finally, and honestly most likely given the temperature change, have you double checked your enclosure parameters? AKA is the basking spot, warm side, and cool side still ideal for a beardie? My experience is that I need to change my heat source from a 75 to a 50 watt bulb for the summer, then back again for winter to prevent my BD's enclosure from getting too hot/cool, despite the fact that my interior temps remain much the same.
Good luck trouble shooting! I hope this helps!
Best,
-Ellen