94 Caprice, 4.3L V-8

Please help! I have a 94 Chevy Caprice, approx mileage is 189,000, it's a 4.3L V-8, automatic. It's stalling, not when driving it, but sometimes when you stop. It's "jumping" when you are stopped and occasionally when driving down the road. It's leaking anti-freeze, but we can't tell from where. There is a little bit of black smoke coming out the exhaust. Power steering gets tight also sometimes. The fuel filter, alternator, plugs and wires, distributor are only approx 2 months old (brand new when purchased). The fuel pump is only about a year old. Any help you can give is soooooooo greatly appreciated!

Thank you so much! Melissa