GT scores, water confidence, map reading and more.
Units that require a 110 GT score which is what is required for OCS, are already eliminating quite a few people, and my memory is that the Special Forces used to require a 115, back in the 60s and early 1970s.
Currently 107 or higher GT score for Ranger and 107 or higher GT score and combat operations ASVAB score of 98 or higher for SF.