air or fuel, what am i running out of

If it feels like it "hit a wall" as you describe and it's a sudden drop in power it's more likely a fuel or spark issue. If it feels more like the engine just gradually pushes less and less as you rev it higher then you're probably running out of airflow.

If it's possible maybe try letting off the gas for a second as you're winding it out in 2nd gear say around 4500 RPM, then get back on it hard and see if it pulls any differently. If it does feel different (wants to pull to higher revs) then there's a fuel issue somewhere.