Dodge Repair: 01 Dodge Durango: rpm rises/code 0420

Question
QUESTION: I have an 01 Dodge Durango and for the past 2 days I have noticed that when I'm driving and get up between 60 and 65mph my SUV hesitates and revs up till about 300rpm's for couple of seconds but when I'm over or below those mph's it runs fine.

ANSWER: Hi Gene,
I assume this has an electronic automatic transmission. If that is the case then the best approach is to use the self-diagnostic capability to find if there is a fault code that the transmission control module had logged into its memory which will give an indication of the problem and then based on the manual what are the possible fixes. Try the ignition key to get the code: turn it "on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the odometer window on the cluster to see if the mileage reading is replaced by a 4-digit number preceded by a P. Let me know what shows up and we'll go from there.
Please see the PS below and respond to it.
Thanks,
Roland

---------- FOLLOW-UP ----------

QUESTION: I did the diagnostic testing you said and got the code P0420 where odometer window is.

Answer
Hi Gene,
That 0420 code relates to the engine, not the transmission. It says that the efficiency of the oxygen sensor on the right side cylinder bank is either degraded, or there is an exhaust leak on that pathway. or the catalytic converter is damaged/worn out, or something is wrong with the cylinder function of the right side.
With no code for the transmission having a fault it is difficult to know what to make of the rpm situation you described. Does it seem to be downshifting when that happens, or is it slipping in gear? I would keep checking for a new code in the 700's or 1700's which are where the transcodes are located. Then let me know.
Thanks for the rating and nomination.
Roland