It takes 3 things for the engine to run. Fuel, spark, & air. You have air, and the truck turns over so you are missing either spark or fuel. You have to find out which of those you are missing.
You didn't find the problem yet.
do you mean it cranks, but will not start?
are you getting spark?
You are missing fuel or spark.
Maybe your fuel pump
Replace the coolant temp sensor.
I would replace the ignetion module that is in the distributor.
I need to know why do i need to crank my chevy truck to start ?
Replace the engine coolant temp sensor.
you should try to poo in it
change your fuel filter and test the fuel pressure. pump pressure 60 psi line pressure after the fuel regulator on TBI 11 TO 13 Psi.
Start clockwise: firing order is 18436572