You seem to have covered a lot in your post, but left me wondering... did all the prior issues get fixed and if so, what was replaced/repaired?
If you have a random misfire, no codes, you likely feel the misfire when at low rpm. It is very difficult to feel a misfire at high rpm because it is so hidden. Given low rpm, is it a 'hard miss' that occurs steadily, can be noted in the exhaust sound, or is it an intermittent that more or less comes and goes? A hard miss would lead me to walking disconnect the injrector leads one at a time and check for cylinder drop/contribution. There may be a contribution test available in diagnostics that will chart the 6 on a graph so you can see which are not doing so well. A soft miss is harder to Dx.
Have you checked fuel pressure? Do you have a problem with high demand, such as hill climbs or accelerating hard?
tom
If you have a random misfire, no codes, you likely feel the misfire when at low rpm. It is very difficult to feel a misfire at high rpm because it is so hidden. Given low rpm, is it a 'hard miss' that occurs steadily, can be noted in the exhaust sound, or is it an intermittent that more or less comes and goes? A hard miss would lead me to walking disconnect the injrector leads one at a time and check for cylinder drop/contribution. There may be a contribution test available in diagnostics that will chart the 6 on a graph so you can see which are not doing so well. A soft miss is harder to Dx.
Have you checked fuel pressure? Do you have a problem with high demand, such as hill climbs or accelerating hard?
tom