93 Camaro 3.4L V-6

I'm trying to help a friend. The problem is that the car runs great on flat land or downhill but when he hits a hill it loses power badly. It slows to a crawl. It smokes like black smoke & you can smell raw gas. He has changed plugs, wires,all 3 coil packs. He cleaned the throttle body with carb cleaner. He said the problem started when he cleaned the throttle body. Please help if you can. Thanks.