73 maverick having problems !!! Help!
 

I have a 73 maverick with a 200ci. The motor was recently rebuilt, and when they rebuilt the mechanic said the transmission looked rebuilt also(but who knows if that was true). So I have a problem when I'm coming to a complete stop. At a complete stop it will want to lose power or it will completely turn off on me when im at a higher speed and if I have to stop sudden. I Have no clue what it could be and I need to fix it cause it is my daily. Also in traffic I'll have to put it in nutrual if I don't want it to die , then put into drive really quick. It is drivable and I've learned to drive with it but it is a hassle, and it shold not drive like that. Any advice ?

Would like to get a little more info.
Was the problem present before the engine was rebuilt? This goes back a bit and it's gonna be tough trying to remember those engines. Some had dist with dual vacuum advance and retard. Does the vehicle have air conditioning?
If I'm not mistaken they had an idle stop solenoid that was energized when the key was turned on and when the key was turned off it would allow the idle speed to drop down to prevent "engine run on/ dieseling". If it does have that part it could be defective, or not connected, or not adjusted properly. If a vacuum hose came off and allowed a vacuum leak it would cause the engine speed to idle high.
Can you provide some more info as requested earlier?
Just for my info, approx what part of the country might you be located?