1966 Mustang 200ci rough idle when in gear

Whenever I put my auto trans in gear, tne 6 cylinder 200 ci engine in my 1966 mustang starts to run very rough. It doesn't apear to have a vacuum leak, and I have changed and checked everything I can think of (plugs, wires, points, condenser, spark coil, pcv valve, fuel pump, fuel filter; the carb has been rebuilt and other carbs have been tried in its place; I've tried moving the timing around; I even swapped heads with a spare but with no noticeable improvement.) It runs fine as soon as I start driving it but it roughens up as soon as the car slows to a stop. Any ideas on the cause??? I'd appreciate any help I can get. This is frustrating! ---Andy

It may just be a trait of the inline six i have a 66 mustang also and it runs quite rough at idle too and then smooths right out when you start driving

http://fordsix.com/forum/index.php

Go here!! I am a member (Natestang) and the members there are veryknowledgeable about the 6 cylinders. JUST REMEMBER 6 can equal 8!!!!!!