97 xj reving high and cutting out.

[onebigmj]

My 97 xj 4.0 cuts out once in a while. It acts like its running out of gas but when I push in the clutch it revs up like normal. It got progressively worse and I was told it might be a cps so I replaced it. It seemed to get better but not go away. It also started reving high but it only does it while moving down the road. If I come to a stop it idles back down. It throws the codes 12 42 and 21. I know 12 and 21. 21 is because my cat is empty and the down stream O2sensor is bad but I was told it doesn't have any effect on the way the vehicle runs.

Sorry for writing so much

Thanks in advance for any help