2000 Blazer
 

Vehicle shut down at 75 mph coasted to side tried restart no power at all checked battery post broken off.Replaced battery but no firing only failed attempt to fire.Have fuel and pressure.No tach movement when engine turning over.Gave a shot of eiyther started in a violent idle that roughly idled truck for 10-15 seconds as what could be dieseling or mistiming.Thinking crank sensor but don't know or have had battery just disconnect on vehicle before.

You need to do a more accurate fuel and leak down test.
If it was a crank sensor problem it would not start. Unless its hitting the reluctor then it would misfire and have a jumpy tach.