97 7.3L PS, tried to start this morning, check engine light and wait to start light flashed continuously ran like hitting on only half the cylinders then stalled. This has never happened before. GP relay has been replaced and i know glow plugs need replaced. Have had no starting problems this summer. Talked to garage they had no idea. Did say the flashing wait to start light was very odd. Came home from garage tried to start truck again same thing, then smoothed out it ran fine. Any ideas? 120K on truck.