1996 Chevy Suburban Ran like new,,,,until

I bought a 96 model Chevy Suburban about 2 months ago, and until last night, it's been running like new(even with 180,000 miles on it). Last night it suddenly developed a knocking sound on top of the motor, was running extremely rough, would not go above 30 mph, and started smelling like it was not burning all the fuel. Any help you could provide would be greatly appreciated. Thanks