Harsh 1-2 upshift & check engine light

I got a 2000 Volvo V70 XC Turbo about 2 months ago. It has just over 100,000miles on it. I had to replace the radiator (ouch) and after I got it back a day later the check engine light went on & will not go off. It is still jerking into 1-2 upshift, though less & sometimes not at all after its warmed up. My mechanic said he can’t do anything 'til I take to a Volvo dealer to do software download to turn off check engine light. My parents bought me the car. I haven’t told them about any of this cause I feel bad they may of put their good money into bad. Anybody have similiar situation and how did you handle it & how much did you have to spend in fixing?