got an ol 73' d100 with a 318/727, that stalls when put in gear. motor idles and takes throttle just fine in Park or N. haven't a clue what is causing this.

 

Vacuum leak or torque convertor. Check all your vacuum sources for leaks.

 

I agree with bremereric, sounds like vacuum leak, a easy trick to help find it is to start it up and use a can of carb or brake clean and start spraying around intake pay attention to the idle-if the idle starts to go up or it dies figure out where you were spraying the cleaner when it died, if its something like a intake leak this will help point it out-hope this helps-also when you put it in gear try to do it without holding it back with the brakes or depending where you live maybe let it roll a little in nuetral then pop it in gear, if its the converter it probably wont die if you are moving when you put it in gear.