1996 Chevy Corsica

I got this car about 6 months ago. I drove it from sacormento from redding, ca. About a 3 hour drive. And it drove fine. And then I went to my work and back and it broke a gasket. Not the head. Just the gasket. So my uncle who is a certified mechanic for chevy came and fixed it. And then now it is acting really messed up. It is blowing out black smoke and eating gas up VERY bad. And lets say you going 40 mph. And you going steadly with. Well it starts surging very bad. I don't really know if this has anything to do with it. But I notice right when it started to happen my temp. Gauge drop. It is not getting hot though. I have also put in a new filter.