Fire blob26

I've had my Rx8 for awhile and I'm having issues with it, issues that hadn't come up in the past 6 months. It seems whenever I drive 4th gear gets very little gas and revs, it won't go above 3,000rpms unless I'm on the highway and going 70mph+ and it has to do to sustain the speed. Whenever I go up a hill(even a small one) 4th gear kinda fails and it switches down to 3rd gear sometimes even 2nd. It happens even if I don't step on the peddle any harder then regular acceleration. Was wondering what could be wrong, my check engine light it is on and is giving me numbers about the computer? When I just got the CAT converter replaced because it wasn't breathing correctly. Any suggestions would be fantastic!

Mysterion

If the CEL is lit, first step will be to attach a code scanner and retrieve the code(s) that caused the CEL. Oce you get the code(s), post it/them here and perhaps someone can help track down the problem. Whatever you do, though, don't drive the car any more or harder than absolutely necessary in case it is a serious error that could cause damage to the engine. Plan well and phone around to see who can retrieve the code(s) if you have no OBD II scanner (some auto parts stores will do this for you, as will the dealer, if need be)