Frank,
You now have 3 threads started here for your tractor. I think it would be of best interest to only have one thread and it would be best if you would have laid out all of your symtoms in that one thread. It is kind of hard to read all three threads especially when all three probably relate to the same thing.
No to your troubles, if it was me, I would take it back to the guy that did the rebuild that you talked about some place and tell him it is not fixed yet or take this one in to mechanic that is familiar with this tractor or engine. It seems you have checked everything that could lead to your troubles and I am somewhat convinced your troubles are of a ring not seated or a valve not seating properly. It may also be in your pump or an injector.
Just my opinion for whatever it is worth.
murph