This simple tip which I have mentioned before deserves it again. Most every rider has a weakness in all 3 riding disciplines. Time trialing, sprinting or climbing. You all have been in the position of being the last rider to get to the top of a climb at one time or another, only to be gapped when that heart of yours at between 150-180 bpms says please stop. And of course catching back up to the group at this point is nearly impossible.
So, I've got the remedy that can help. Before you get to the climb position yourself if not at the front, close to it. That way as you drift back being passed by other riders hopefully you won't be at the back when the climb ends. For steeper ascents try and not look at the top. Concentrate on what's 10-30 ft. in front of you. Also standing if possible as long as you can, and keeping a smaller gear vs. a larger and higher rpm's will also help you improve this weakness. Practice, practice when you are out on a solo ride!