I have a 2000 GXE and I just returned from a trip and my tranny was acting funny.
My car was in overdrive and it shifted back raising my RPM's. That was after running at about 75-80 for about 65+ miles. I pulled over and parked it checked my fluid and after that i got back on the road. No problem after that.
But I have been noticing a high rpm before it kicks into overdrive. Over 5,000 rpm.
My mechaninc pulled a cat code and I am curious as if this could cause that type of hiccup.
My last question to the ORG is what is recommended a regular drain and fill on the transmission or a power flush. Should I replace tranny filter before doing either.

 

It probably overheated which takes it out of OD. If it's <100K flush it, otherwise just change it. You might want to consider a transmission cooler. Is your radiator original? The cat code is not related. There is no need to change the screen (not really a filter).

 

I will have the change done this week. I am not big on mods so a tranny cooler sorta eeks me out. Dependent upon on how it acts after the fluid change I may consider it.
I did a sea foam treatment for the first time and I see a big difference in its throttle response. I am going to clean my MAF sensor today and then change the tranny fluid. I will update and let everyone know how it turns out.

 

Good advice here...drain and refill tranny fluid and see how the tranny reacts. If you still have problems then do a complete flush. If you still have issues after that you might want to check into a tranny cooler.

Your transmission symptoms are from it overheating. The exact same thing happened to me two times. I pulled over and let it cool and it was fine shortly after.