I have difficulty with some matchps, but I know I'm not as good of a Rumble player. I also don't play midlane Rumble [I can't get away with that in EU Gold level. It's not like people care that I know some very very high level player on NA who mains it].
I have difficulty with Shyvana, but I've not actually had that matchup since her nerfs. Characters who are particularly mobile are also issues, such as Udyr, although this is more 'I can't kill them'. Jax is also annying, since his Counterstrike reduces the damage of Flamespitter and Equaliser while active, and then he can leap-stun me, and he also has his ultimate, but I don't outright lose to him until 6+.
Nasus' sustain and Wither can also be annoying and lead to me being outscaled. Wither is also very annoying when I'm ganked because well... Rumble has relatively low mobility. But Nasus is more a deal of don't over-extend while attempting to zone him.
But yeah, I really did not expect to stomp Yasuo. Especially since this is actually my 2nd time directly laneing against Yasuo [I don't often play mid/top...]. However, Flamespitter would tickle him and activate his passive, I'd wait for the barrier to fade, and then go aggro. Wind Wall didn't stop Flamespitter as it's not a projectile, it's an AoE, and Yasuo would then be chased away from dash targets giving me a clear shot for Harpoons. [This is also something I'm generally working on, createing situations I can take advantage of later and forceing the foe to do something that don't want to which I can capitalise on. Basically, thinking a step ahead.]
Got to the point I could trade a kill on the enemy jungler in a 2v1 situation.