A lifted Jimmy can be a Hot Rod if that's what you want for a Hot Rod!!! Welcome to CHR! You might try pulling the plug wires one at a time with the engine running. If the engine doesn't stumble or at least slow down when you pull a particular wire, that would be the problem cylinder. What is the condition of the rest of the ignition system????

Another real good place to start is with either a leak down check or a compression check!!!