Help

[LOW1TON]

Hope you guys can shed some light, My dually is an 88 r30, it has a 4 speed, 454ci with TBI. My problem just started, when I first start my truck up it is running very rich to the point it will burn your eyes if you stand to close for very long, it idels pretty smooth and will maintain an idel without any problem, while it is ideling it will show some smoke from the exhaust very little but still some comes out. If you drive the truck for any extended period of time when you come to a stop it will idel down very low and in most cases stall out, it will start back up with no problem. I have already replaced the MAP sensor and the coolant sensor and that did not solve the problem. I am looking for ideas on what else it could be. I just started this almost like a switch was flipped, Both of my gas tanks are brand new with new pumps and screeens in both tanks and my tank selector switch is also new. Any help would be graetly appreciated. Thanks in advance.