[dr pepper]

if it is not an ignition problem then it sounds as though the auto choke is going to be the issue, what to do depends on whether its a weber or pierburg carb, a new carb from a scrapper could be good if you can get one cheap.
some sierras have sensors on the water jacket and inlet manifold, check the connections to these, i'm not absolutely sure what these do, but ignition advance cold starting is quite likely.
sean.