'99 Lincoln Town Car, when I put it in drive it cuts off in a few seco

Have you determined where the gas smell is coming from? You need to first determine where fuel is leaking from as this is your main problem. As to it dying when putting it in drive it could be either to much fuel being dumped in or to little fuel, either will kill the engine. As to finding the leak you need to check the fuel filter, the entire fuel line and the tank itself. a break in the fuel line can either dump gas on the ground (place cardboard under vehicle to help find leaks) or suck in air which messes up the fuel/air mixture. A hole in the top of the tank allows air to be sucked in through the fuel pump.