Why does engine die, after putting it in gear? reverse & drive kills it

What is your question?

Truck starts up good; once put in gear, either reverse or drive--engine will die. Also, using more gas; cold check of tranny oil shows over full and warm check of tranny oil shows it is low. No catalytic converters; been used on family farm. Any suggestions appreciated; please give location of part to be checked, so I will be able to find it. THANKS