Probably all the advice you need has already been given, but I'll add my $0.02

1. 400 miles/month just isn't enough to build real cycling fitness. At least when the days are long if you really want to improve your skills, 800 miles/month is more like it. You don't by chance have a job or something inconvenient as that do you? Absolute minimum, I would say, is 600 miles/month to get in halfway decent shape.

2. It's not impressive to do 25 MPH in a double pace line if you're not spending appreciable time on the front. Fun as hell, yeah, but not any kind of measure of your skills.

3. If during the climb you are switching back and forth from high cadence to low cadence, then you don't really know how to climb hills yet (unless the switch in cadence corresponds to getting in and out of the saddle). We could give you all kinds of advice, but you just need experience and advice is no substitute.

4. Hill repeats. Hill repeats. Hill repeats.

5. Yeah, some people never get good at hills, but from your account, you're probably not any where near your potential yet.