Idle high and dips low?

The rpm dip low constantly and the car acts as if it wants to stall. Rough uphill and definitely difficult to get it to highway speeds.
What I've done
- changed out both catalytic converters and the downstream 02 sensor. The upstream 02 sensor they ordered was wrong so it's disconnected but the problem was before this.
- Checked for air leaks at the intake and manifold. Manifold has a small crack but I don't think that would cause this?
Any ideas would help out significantly. Thank you guys for your time you are awesome!