The way I always checked for a bad cylinder/injector when I worked at the John Deere dealership was to get the engine thoroughly up to operating temp. and then set it to idle. Then break torque on each fuel injector line enough to allow a dead miss to occur. The cylinder in which nothing happens when you break torque is more than likely the bad injector if it is being caused by a faulty injector. At that point I would shut the engine down and pull the injector and take in back to the hand pump injector tester and check it for popping pressure and spray pattern. As already mentioned, you want to double check all of your injector line fittings for tightness. If you find a loose fitting, typically 1/3 wrench arc after fitting seating is proper torque or at least a good ball park torque. How much smoke are you getting once the engine has rev'd up to full pto rpm and fulling warmed up? Could be an oil control problem. The other issue that can cause what you describe is if the engine spend excessive amounts of time idling, especially is very cold weather. This can cause "wet stacking" which is a big no no. Basicly carbon and incomplete combustion by products build up on the exhaust valves do to low cylinder temps. and exhaust gas exit velocity.