I agree. You need to check the Transmission and Differential to make sure everything is okay. On most r/c cars, the Diff will fit in the diff case either way. If the differential is installed with the big gear on the left, for example, and you remove the diff and turn it around so the big gear is on the right.... Now the car will run backwards.

As for the stalling.... Is that .15FE brand new? If so, the rich break-in settings can make it hard to start. You can try a hotter glowplug for breakin (what plug do you use now?) or you can lean the mixture screw about 1/8 to 1/4 turn to get the engine started. Once the engine starts and warms up a little (about 30-45 seconds) you need to richen the screw back to the original breakin settings to safely complete the break-in procedure.

Also ensure that your glow heater is fully charged (if rechargeable) or has a fresh battery if it uses regular batteries. A weak glow heater can make any engine difficult to start.