Personally I feel J65 actually runs BIG, not small. But I never tried my TTS so I can't say for sure. For reference, I am usually sz L, and I tried and could fit sz S (still ok with a tee inside, but I would not be able to wear a hoodie), tried sz XL as well and it was just WAY too big (I imagine I could fit a hoodie AND a shell inside and still have room). However the material may actually shrink (?) if you wash it... so maybe it would fit tighter down the road, I am not sure.
Has anyone noticed the pants have different sizing from earlier seasons e.g. pre-2016? I own an older P17-S and it is a sz L. In the waist measurement, it is actually the same as a 2018 P23A-DS sz M. I do not think the difference is because of the materials... For the P17/P23 styles (extreme large waist), I suppose it wouldn't matter much, but I believe the same "difference" exist in other pants like P10/P24. Can Anyone verify? It is especially useful to know when we order "over internet" as sometimes we just order by the same size of an older item, thinking it would fit the same... (Non-ACR references: Nike ACG line in recent years, the pants have gone a size larger than before. Similarly Supreme gears)