I have a 2003 durango 4x4, 4.7 lt. engine. my check engine light came on and I am getting this code while doing a self diag. check can anyone help

 

P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)

I'm thinking maybe a new cat converter will take care of your problem, go to a muffler shop and get a new one. Since you have to do it anyway get a high flow cat, it will make your D more efficient (probably only slightly but still an improvement).