First and foremost for a hardgainer and/or ectomorph is eating lots of meat. It will simply increase your gains so much. And I don’t mean skinless fatless chicken breast. Beef, bison, buffalo, dark meat turkey, snake, kangaroo, fish, lamb with all that yummy fat. Calories are your friend.
Second is eating as much as you can day in and day out. Week after week. Consistency in eating high quantities of high quality food is as important as your consistency in the gym. You are very slim at 175 and 6’1".
Third an ectomorph/hardgainer must do everything they can to maximize testosterone and recovery. You can do this by eating more fat, specifically saturated fat and monounsaturated fat. Make sure you are getting enough zinc and sleep. Olive oil and avocado are good sources of monounsaturated fat. Whole eggs are good. No egg whites.
Fourth, you may find the supplement Alpha Male very helpful. I find it helps my muscle mass gains, improves my appetite, keeps my testosterone levels high, increases my recovery and keeps me leaner.
In terms of a program, as a hardgainer/ectomorph you will need to change the stimulus every three months.
Most important, regardless of the program is it gives you results i.e. you are getting stronger and your body composition is improving. You can do more volume as an ectomorph/hardgainer but you must use it intelligently. Pay attention to your energy, drive, motivation, performance and recovery. If you are using higher volume workouts keep the volume to compound exercises i.e. pull ups, dips, deadlift, squat, overhead shoulder press, rows, not 6 sets of bicep curls.
A1. DB overhead Shoulder press 8 reps
B1. DB Row 8 reps
A2. DB overhead Shoulder press 6 reps
B2. DB Row 6 reps
A3. DB overhead Shoulder press 4 reps
B3. DB Row 4 reps
C1. Barbell overhead Shoulder press 12 reps
D1. Cable Row 12 reps
C2. Barbell overhead Shoulder press 8 reps
D2. Cable Row 8 reps
C3. Barbell overhead Shoulder press 3 reps
D3. Cable Row 3 reps
Increase the weight from A1 to A2. Increase weight from A2 to A3 etc. Record your workouts and focus on getting stronger and lifting more weight at those rep scheme. You do not need to lift to complete muscle failure every set.
Gaining muscle is an art and a science. Put your attention to it and you will get results.