Engine Performance problem
1988 Dodge Truck V8 Four Wheel Drive Automatic

Has a new 5.2 litre engine with only 3,000 miles. Problem existed before engine change over. It does show a code #37, which is, torque converter clutch solenoid circuit. Trans. is completely re-built and converter replaced. Here's the problem.
You can drive the vehicle on short hops and everything runs pretty normal, but it should run even better with a new engine. When you are on the freeway, at freeway speed for say over 30 minutes and go on to an off ramp to idle down, it won't idle down without feathering the throtle, it wants to die. If you get it started again, it runs real rough, lots of black smoke. If you were to let it sit for 30 minutes, it will start up again and run fairly normal, will do the same thing again if you take the same route back. Been doing this for a long time. I had an appointment witha Chrysler dealer this morning and they stood me up, so I'm back taking care of it myself. Please help me out!!11