5.10 is my limit, both trad leading on the rock and in the gym.
I do not have the strength or the technique to climb harder grades. If I climbed more consistently and trained specifically for climbing, I am positive that I could improve my ability in the gym. I think it would be a slower amd more difficult process to try and improve my grades on the rock.
I was able to improve my trad leading by doing a lot of gear placing, to the point where I am confident in my ability to protect a route. I them rationalized to myself that I can climb 5.10, and I can protect it, so therefore I can lead it. I basically forced myself up routes this way, and my confidence has followed.
I think that DFA had it right when he talked about being pumped as a mental problem more than a physical one.
Climb with better climbers, or if your partners are at the same level, get competitive and push each other.
Develop confidence in your ability to protect routes, and don't worry about using the gear if you are trying to advance, the clean ascents will come with time.