@wmsgil I think you have the discipline and consistency part covered, which is the majority of it. A standout to me is the training and using preprogrammed routines. Also I think you need to prepare to gain more weight, which might mean getting a little bit fatter than you like. EDIT: I misread, ignore "You did a really good job of a clean bulk, but I would have jumped into a maintenance phase for a bit then pushed it a lot further."
I wouldn't worry about your strength much, I'm an ex powerlifter and the biggest strength gains I had were after cutting out the big 3 entirely and focusing entirely on hypertrophy training and gaining size. Program for hypertrophy, track all of your lifts, focus on the stretched position and technique. If your lifts stagnate, try chasing soreness for a little bit to see if you might be doing too little.
EDIT: You mention you're a recovering volume junkie, you may find cutting this back significantly results in more progress. You adapt to the workload you give yourself; this might mean you can do 20 sets of hamstring work before you reach muscular failure, cutting this back after a nice deload and trying to focus on quality could result in more growth and soreness from 5 sets instead.
I also wouldn't worry about your T levels, everyone has low T symptoms from time to time. You've built a great physique with those levels. The caveat is it may be more difficult to cut to stage conditioning without losing muscle. The following is entirely anecdotal and may not happen to you; my natural levels hovered between 350-400, and I had a lot of issues with joint pain, and muscle loss always occurred disproportionally below 10% BF. If your goal is to be a successful natural bodybuilder, the reality is you may not have the genetics to get there. If that isn't your goal I wouldn't even think about your test at all, and even if it is there is nothing you can do about it naturally.