It's going into limp mode for the transmission since the RPM's are higher. That is a 5 speed automatic (545RFE) and when it goes into limp mode, it goes back to 3rd gear and stays there. My 04 Dakota kept doing it. It set a P0700 and a P0750 code which was shift solenoid malfunction situation. I had a new one put in and it fixed it for a while, but it came back. Had a new rebuilt transmission put in...and it came back! :BangHead: I checked all the wiring for bad spots and it was fine. Only thing left was the ECM, which has the transmission control module integrated into it. I hail Mary-ed that as a last ditch effort, and swapped in a remanufactured ECM, and it ain't done it since.
That was my troubles with the same transmission, so yours may be different. You can go to Autozone and get them to pull the codes, but they won't be able to reset them for you. You may also be able to click the switch on and off 3 times real quick, and it will display the codes where the odometer is. You can disconnect the negative battery cable for a few seconds and it will turn the check engine light off and reset the codes, but won't fix the problem which may come right back as soon as she gets up the road a little ways.
Good luck with it. It can be a pain to figure out exactly what it is!