Help, My car is driving me crazy

I have a 1996 mercury villager with 125,000 miles on it and since moving to orange county 6 months ago it has given us nothing but problems. We had it at a mechnic in November, literally the month of November, (I even joked that it does not like Orange county). He unplugged wires, cleaned out the fuel injectors, put in a new oxygen sensor and the check engine light was off, it did not work, they fixed that, the problem still persisted even thought they assured me that it was fixed, then took it to a transmission guy, they found a leak in the transmission hoses and they fixed that. The car worked for 2 hours after that then it started again. Let me try to explain the problem. The car is fine when cold once it gets warmed up the problems starts. I am driving 55 smooth sailing as soon as I stop at a light it has a problem picking itself back up to 55 and starts sputtering, (like it's telling me, oh you want to go now, let me think about, then the gear kicks in and it goes off again until another red light and it does it again. Took it to autozone and they told me that it was a Random Cylinder misfire and gear 1 and 2 ratio [/b[b]]incorrect. What does that mean? We thought it mught be the sparkplugs or are we just being naive. Is it worth fixing at this point we need to inspect the car but it cannot pass inspection with the light on but we have spent $2,000 already fixing it.