99 Ram 318 stalling

My 99 Ram 1500 runs great except if I shift to neutral and coast. While driving home from work right before I get to my exit on the highway, I will put it in neutral(auto trans) to coast about a half mile to my exit thinking I'm saving gas. I will do this at 65-70mph and as soon as I put in neutral the tach almost immediately drops to zero and then stalls. I still have lights and radio, but no power steering of course. Then I come to a stop and it starts right up. However tonight, it cranked for a second before it started and the lights dimmed as it was turning over. The obvious would be to not put in neutral and coast, but is this normal? If I am already at idle speed and go to neutral it is fine. Please, any help would be appreciated.

Leo
99 Ram 1500 4X4 5.2