Leak-down of fuel pressure fairly common on Gen I RT/10's...our 95 had new pump replaced under warrenty.. if you turn key on for several seconds, then off, then on again(2-3 cycles) to allow pressure to build up, and then it starts, could be you have a similar problem...get it checked as soon as you can. I would be interested in what others have to say, especially on a 99. Good luck.