Gaining lean muscle on 500mg test/week?

Hey all, I've been trying to build lean muscle for a year now while running 500mg of testosterone per week. I'm going to keep using it because I feel great and haven't noticed side effects. I put on 6 kg while maintaining the same bodyfat, but I've stalled for about four months — only gained ~0.5kg in that time. Currently eating 3000–3500 kcal and ~200g protein daily. I began the bulk at 2500 kcal and slowly increased. Training an upper/lower split five times a week. I don't want to add other drugs or raise the dose, so what would you suggest to push progress again? I'm sure others have faced this, curious about experiences.