It could still be the injection pump. I had same problem and it had to do with some disks or something in pump that tells which injector gets the high pressure fuel to fire injector' The disks were corroded and the fuel would leak out the pressure to other cylinders and not fire the injector that it was supposed to fire. not sure what the parts are call desilcrawler probably knows.
distributer valve or plates

 

yes but after it fires its fine,I called Spenser diesel and he said that the advance piston may be sticking,if thats the case he will install a new piston plus install a metal sleeve in the bore,will see