2001 powerstroke won't rev past 800, white smoke from exhaust
 

New here, looking for some guidance. My brother bought a 2001 7.3 with 215k miles on it the previous owner said the truck broke down without warning and he had it towed home. He changed the oil and oil filter and fuel filter and icp sensor with no luck and then sold the truck. Since getting the truck I changed the drivers side injector harness/valve cover gasket after getting a code p1294 from a buzz test, the harness had high resistance on the injector common circuit. Now the truck does idle better and I could watch those drivers side injectors squirt oil. But it still smokes and won't rev so I did a contribution test and it came back cylinders 1, 3 and 4 bad. I'm new to diesel but I'm good with a multimeter and a good friend loaned me a scan tool. Where should I look next?