1999 Ford Mustang Car is bucking when driving

I just replaced the intake manafolid on the car due to the gasket was leaking. All the connectors were hooked back up. Car was running awesome. After about 2 hours later - I was driving home from dinner and I felt the car buck while climbing a hill. It than felt as those something was miss firing. I pulled over and checked things, and all look well. I have been told it maybe a coil or a fuel injector - how would I know for sure. I was even told it could be bad gas?

started idling rough and miss firing in the 1000-2000 rpm range.

Please help. Thank you