Sell it and buy a GT4. I had the same problem when i got my first gen 6 GT almost 10 years ago now. was fine for the first couple of years but then started to get a bit stale. I sold the car on and replaced it with another brand the lasted less than 6 months hated the car and returned to another gen 6 GT. Over the course of 10 years i have returned to the Gen 6 5 times in total and once to a gen 5. all for the same reason non of the cars i replaced them with could come close to the look, feel and practicality of the Celica`s. The cars i had inbetween were Clio 172, Prelude VTI, Corrola Tsport, (cheap motoring Escorts mondeos couple of civics VTI`s) all the the cars lasted less than a year before i was jumping back into a celica. The latest was the Tsport but that made way for a gen 6 GT4 and i`ll never look back.
The GT4 hasn`t been perfect and has required abit of work and some money but it was to be expected for picking up for cheap cheap. The car drives great now and always puts a massive smile on your face on boost.
All the best and good luck in your search for happyness