Don't know about the Durango. In the Viper, there are two sets of O2 sensors, one before the CATS and one after the CATS. The O2 sensors produce a signal that is tied to the computer (ECU) that tells it that everything is OK. This results in the computer allowing an Air/Fuel mixture that is suitable for the condition being encountered. (like hard acceleration) If the O2 sensor does not deliver the appropriate signal (in volts) back to the computer, (which it won't if the CATS are missing), the computer richens the mixture to insure a 'safe' A/F condition (not lean). Although the 'rich' condition is safe, it certainly is not conducive to making max power. The trick is to fool the computer when the CATS are off. This requires an O2 simmulator that plugs into the connector that the O2 simmulators plug into. The O2 sims produce the signal that the ECU requires to lean the A/F mixture out and provide max smoke. The trick to this is getting the right O2 sim that duplicates the signal that tells the ECU to 'let'er rip'. Call Apex, tell them what you have. Either he'll have the sim that you need or he can tell you where to go to get it. Since this is a Durango, Jerome may be right (although that would be a 1st) and Jegs or Summit may heve them. I'd call Bill 1st though cuz I swear, he's the man!
Hope this helps. If not, you're hopeless and you should be driving a Volvo. /images/graemlins/supergrin.gif