I'm very much the same (except I was never confident of gaining places on descents). I have to push on the ascents.
It can become a self-fulfilling prophecy. If you're always knackered at the top, you'll never catch people on the descents. So you think you're a poor descender and have to put much more into the ascents... and the cycle continues.
These days I put it all down to fitness. If I'm fit enough to finish in the top 10, I will. It takes a lot of pressure off. I still push hard and know my strengths and weaknesses, but I'm less likely to get my split very wrong [famous last words...]