Chain skipping when pedaling hard
So my chain skips a bunch and makes a horribly disconcerting noise when I pedal with a little more strenuous force.
I have a 3 x 9 setup, and it really only happens when I'm in the middle or smallest chain ring, example: in a low gear ratio going up a hill, or just getting going after stopping at a red light.
It led me to believe my chain was too long (just installed brand new chain), and I've since removed some links, but it still seems to be happening. The smaller the chain ring/cog, the more it occurs.
I've checked the teeth of the cogs on my cassette and they look fine. The bike will ride fine if there's no strenuous exertion on the pedals, I've adjusted the derailleurs, everything shifts properly and doesn't make any clicking noises while I'm riding.
What am I missing? It's a really annoying issue and it's preventing me from really going hard!
Please help!