I have a 283, with a 2 barrel carb on top. The engine was running great, and one day it just started running like crap. The problem is that when I jump on the gas in first gear it rev's up to about 3 1/2 and chokes up, Starts back fireing and just dosen't wanna go....same thing in second and third gear too, just different tach readings. If I rev it up slowly I can take it to any RPM but only if I'm realy patient. What could cause this? and how can i fix it?