Highly likely that the magnetic sensor on the ring gear is bad. They get flakey when they heat up. Some people refer to this sensor as the crank position sensor. It is located on the left side of the engine where the bell housing meets the block behind the cylinders. Difficult to get to.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k