It's as simple as benching more frequently, frequency > volume for lagging muscles, just add the volume as you go at your own discretion. You need to keep things as simple as possible. Barbell Bench Press, Floor Presses, Spoto Presses, Overhead Presses and close-grip bench presses should help your bench shoot right up, keep the isolation exercises at a minimum.
I also noticed you said you were improving on incline dumbbell pressing but not flat barbell, it could also been form related. Take a suitable grip, relative to your shoulder width, not the markers on the bar, protract your shoulder blades, create a lower back arch, utilize your triceps properly. When you hold the bar, it should feel like you are grasping it to benching it. Don't flare your elbows out either, keep them somewhat tucked, but not so tucked it emphasizes the triceps too much.
Look into Johnny Canditos Upper/Lower routine, he's a well accomplished power lifter with a great deal of experience who is extremely strong.