I didn't read all the replies, but I have a few comments.

Are you changing to an easier gear when you climb?

Are you pedaling efficiently, pedaling through the entire rotation? I notice the benefit of proper pedaling on hills more than anywhere else. When I'm struggling with a climb and start to focus on how I'm pedaling, I often start going faster.

Also, as for getting stronger, both for climbing and riding in general, intervals will help a lot. I like to do intervals on a specific route at specific locations. I'll hit my lap button on my Garmin and ride as fast as I can from a specific spot to another (usually between two intersections). I typically do my intervals on hills. I hit my lap button at the end of the interval and try to do it faster than previous times. I keep track of all my intervals. If you're not used to intervals, two minutes can be a LOT if you're really pushing all out (which is the idea). So you might start with 30 seconds or a minute and work your way to two minutes or longer. Then ride super easy for a while in between intervals. When you push yourself at an intense rate for a short period, it makes riding a not so hard intensity easier for longer periods.

I usually prefer doing intervals based on distance, because it's easier than looking down at my Garmin over and over again to see if I'm at 2 minutes yet (or however long I am choosing to go). It is especially hard to do this when standing during an interval, which is another good thing to do (standing intervals).

I noticed a big improvement when I got serious about adding interval rides into my weekly rides. You don't want to do intervals every ride. Your body needs a break between really hard rides, which might be intervals, really long rides, intense climbing rides, lactaid threshold rides (you can look that one up!), etc.