Continuous lag with incline dumbbell press

I made gains with bi/back/tri/even shoulders. Yet I still struggle to get past the 70 lb db's for incline. 5-7 reps.

On tri day I even close-grip 5 sets of 60-70 lb db to hit chest.

I do 15 sets per body part, 3-4 times per week

Dumbbell bench is ok. 80-90's 6+ reps. Much easier to get weight to starting point.

If it is a matter of grip strength? I can feel if it's going to be rough day when I pick up the 70 lb off the rack.

For other dumbbells I use, or work up to

shoulder 60's+ lb press
back 80-90 lb 1 arm row
tri 40-50 lb 1 arm overhead
bi 50 lb alternate curl

They aren't lagging. Be patient and gain weight.

dumbbells are difficult to progressively overload with and you won't up the weight very quickly. Try something else besides dumbbells and gain weight?