I have an interesting problem. My car seems to be running either very rich or has very retarded timing.

At low revs there is almost no power. If I put in neutral and rev the engine from idle in almsot dies. However, if I get it up to about 2K forst, in revs fine.

I've changed everything but the 02 sensor. Could a bad 02 sensor make the timing retard enough to make the car run poorly at lower revs?

 

The O2 sensor would affect A/F mix more than timing but this could affect low RPM power.
You say you replaced everything, what about the MAF sensor; You could try to clean that with CRC MAF cleaner. Another thing that could cause that is a failing TPS, you need a good scope to test that or a swap known good swap unit. Just some ideas.