87 Celica- timeing problem?

Have a 87 Toyota Celica GT. Recently had the timeing reset b/c of power issues. Would get on the freeway and I could feel the car wanting to kick into the next gear (automatic), but was unable to kick into the next gear. Then a min later, would suddenly kick into the next higher gear. I then took the car to a guy who said it was either the timeing off, or the converter. The timeing adjustemnt has helped, but still not totally fixed. I am I now looking at a $300 new converter? :confused: