[geezer#99]

You’re likely only turning 2400 rpm at 65 mph.
Your motor would like to be happier and run up closer to 3000.
You could try more timing.
Try it at 14 and see if that helps.

You could do an easy rpm test.
Try the same hills at 45-50 mph in 3rd gear. You should be near 3000 rpm.
See how the power feels then.