Dodge ram idle issue

Alright well, I'm having issues with my 96 dodge ram again. Maybe you guys will be able to spot the problem because I'm sure having a difficult time. Every once in awhile (like every few months) I have problems with keeping my truck running. I've got the 5.9 with about 80k miles. When it acts up it begins to idle realy low (like 400-600 rpm). I'll start it and it will fire however, when the rpms come down to the idle level they will continue to fall and kill the engine. Sometimes at low speeds when I let off the gas it will die. I can keep it running when I give it a little gas right as I start it up. Once I take my foot out of it it shuts off. If I continue to give it just a little gas and drive it around the parking lot a few times then it will usually stay running but at low rpms. Has anyone ever had this problem before?