Hey Brother, glad to hear that the change in your training helped! Always nice to hear. In the future, if you or anyone else has a question about bringing up a body part, include a very basic idea of what you are currently doing for that part. Understanding what doesn't work for you will greatly help me understand what will work for you!
For arms in general, I don't suggest using heavy weight for low reps. You're already using your tri's with heavy weight on chest day and when doing shoulder presses so too much heavy weight with your direct arm training often leads to elbow problems. When you are directly training tri's, I would focus more on higher reps. I suggest using more cable movements and working with higher reps. I may do a couple of exercies for sets of 12-15 reps and then move to 1-2 exercies in the 15-24 rep range. Yea, I know. Thats really high! But I find tri's tend to respond better to higher reps. See what works for you.
Here is an example of what I might do. Keep in mind that I often super set Bi's and tri's
Warm up first!
Cable straight bar push down 4 sets, 15 reps
DB Skull Crushers 4 sets, 12 reps
Reverse grip cable push down or cable push down 4 sets, 20-24 reps
Maybe finish with a couple sets of body weight tricep dips to failure or a couple sets of very WIDE grip Push downs using the Lat Pull down bar, light weight for 20 plus reps, fast, as this will focus on that inner head.
And Remember, just because these are high reps doesn't mean you should rush through them. You should find a weight that you can do the expercise for the given reps, to failure, and use controlled and mindful form through the reps
Best of luck. Come back to the Q/A and let me know how it's worked!