97 Harbody Stalling problem

[jbtm]

I have a 1997 Hardbody, auto trans, 119K miles. Truck runs good except I have stalling problem. The truck starts up fine in the morning after sitting overnight, but when I start to drive it and, come to a stop the tacometer violently goes up and down and then the truck stalls. It does this for about 3-4 miles and only when I stop. After 3-4 miles the engine has warmd up and no more stalling, until the truck sits overnight and is started and driven the next morning. I can prevent it from stalling at a complete stop, by keeping one foot on the break and one on the gas pedal. Any info as to what could be causing this problem would be appreciated.