I will be honest and tell you that my arms have always grown with ease. At this point in my training, I only train them every other week and they still seem to grow. That being said, I don't know that I'm the best guy to ask. But I will give my suggestion anyway. When I first started I got great results by splitting up my bi and tri routines to dedicate more attention to each. You mention that you have tried pretty much everythingl The only thing I would say to try is maybe squeeze the muscle more and focus on the contraction. My arms always grew from moving high weight and just getting the weight up. Maybe this doesn't work for everyone. All you can do is try a variety of things and iut sounds like that's what you have done. Try and be creative.