Improving consistency

I am a USCF expert level player who hit 2100 a few months ago, then dropped off into the 2000s and have been hovering for a few months now, generally within 20 points. During this time, my record against 2100s has been nearly 100% and I've had winning positions against nearly every master I've played. My problems come down to two things: bad losses against 1900 and under players where I play like an ignoramus, and extreme difficulty in converting huge advantages to wins when even somewhat low on time. Even outside of those two, I rarely come out of a tournament looking like the player I did in the tournament before. Is it just a matter of experience? Is there anything specific I could do to help?