my car has carried a miss from its old engine to the new one. it happens when the engine is under load at around 3K, but it doesn't do it every time i drive it. The tach jumps pretty bad for a couple of seconds then it smoothes back out. The car has a new distributor, cap, rotor, coil, plugs and wires. so i was thinking maybe it's an injector sticking, but i've tried injector cleaner and saw no change. I also don't have an air pump and have headers w/o air tubes, but i still have my egr. I don't know if this could be the source of the problem. Any ideas would really be helpful.
Thanks in advance

ahh yeah.. tpi 350

 

Check the condition of the ignition primary power wiring. That would include the ignition switch and power from the fuse panel or fusible link, depending on the vehicle the engine is in. I just went through this with a '57 Bel Air.

 

Another good thing to check would be the wiring going to the Distributor to make sure it isn't rotted or anything. You could also clean the contact points for the wiring too.