In addition to what cigroller noted, I just have to make the following comments:
The CEL was still illuminated after $800 worth of (unspecified) repairs, and you have not taken the car back to the folks who worked on it? Not a wise decision, IMHO.
The CEL has now been "on" for several months? By now, who knows how many trouble codes might have been stored? You need to have the car's OBD system scanned (free of charge) at an auto parts retailer. Then, you can come back to this thread and post the specific code(s) for more detailed advice.
The transmission is not upshifting? Have you checked the transmission fluid? If so, what did you find when you checked it?
Also, you have not told us the odometer mileage of the car or its maintenance history--particularly how often the transmission fluid has been changed and when the spark plugs, plug wires, air filter, and fuel filter were last replaced.
Taking a total stab in the dark, I believe that you likely have engine driveability problems and--possibly--transmission problems as well. The start of diagnosis is to get the stored trouble codes for us and to fill in the missing information regarding odometer mileage and maintenance history.