While most parts of my body responded quite well to training, certain areas such as upper chest, butt and traps are somehow less responsive. Any advice?
I’m really surprised that you would have trouble with your traps. They seem to be the one muscle group to really respond to training. You would really benefit from reading as much Ian King as possible. Prioritize these muscle groups, ie; traps and glutes first workout of the week. Deadlifts will do wonders for your glutes, hams, and traps if you keep your shoulders pulled back throughout the movement. Upper chest, try incline benches with the bar. Keep your elbows out to your sides and bring the bar down high on your chest. Read the Hise breathing shrugs article that was just in the e-mag.
train them first in your workouts. Use different exercises than you are currently using for them. trying changing tempo and reps every 4-5 workouts.