Is the rotor in your distributor even turning? take off the cap a turn it over to see. I just had a spark problem with my other truck. I check all the grounds, changed the coil, cap and rotor, plugs, wires, ecm, and it turned out that my timing chain was broke and not turning the cam in result not turning the distributor. ended up bending my valves and had to pull the heads. I hope this is not the case for you.