Troubleshooting a ruff idle ?



My 65 stang was running great, then for no apparent reason, when coming to a stop the engine idles very ruff. almost stalls. what would be the order or sequense for system checking. all sugestions are welcomed.
My engine mods are as follows: a 250 head on a bored 200 block, 6 to 1 header, 8mm plug wires, high spark coil.
Recently replaced the C4 transmission but no indications of any problems.
All help is greatly appreciated. Thank you, Mike
Also, any local support? I live in Tracy,California. 20 min west of Stockton or Modesto.
Sounds like a vacumn leak to me....Since you recently installed a c-4 i would start at the transmission modulator and check for leaks. If you dont find it there, get a can of wd-40 and spray around the carb and base plate and see if the idle changes......Vacumn leaks can be a bear to find....ask me how I know

Also if it seems to die when you put the brakes on can be the float is set too low.