We were given a Montero sport with 160K miles on it--we barely had it registered when it started acting up. It stutters and acts as if in neutral when you slow down (like at a traffic light or stop sign). If you come to a complete stop, the car struggles to get going again. The check engine light came on and we took it to the auto parts store for a free computer analysis: the verdict is that there is no code. The in-store re h looked it up and say that it was "missing first gear" when the car is in drive. When manually shifted, the car seems to run fine. Any suggestions?

 

That is strange. If the Check Engine light came on, it will store codes even when the event that triggered it is no longer present. If the light is still on, take it to a different shop and check the codes again. Some of the transmission issues will also set a CEL or a Center Differential Lock light (flashing orange light).
To try to solve the transmission issue, you can start by checking your transmission fluid level. If low - top it off. If the fluid looks dirty and old - do the fluid change and see if it will help. Hopefully you caught the issue early enough that you can get away with something simple and not the transmission rebuild.