Im my opinion there is nothing wrong with Tri-X, it is still a great looking film. However, it is even better with PMK! Try it out.(posted 8414 days ago)You can process film sucessfully at a wide varity of tempertures. PMK and TMax are generally recommended at 75 degrees. 80 is not out of question for PMK, but I would be wary with others at that temperature. You need to be sure that you are correctly compensating for the temperature changes and that your temperature is not drifting to much during processing.
I agree that you may have fixer problems. Are you toning your prints? This can also cause problems it your fixer is not right. If you make two prints from the same negative, at the same time, do both exhibit the same mottling pattern? Does it match exactly? This will help us narrow the problem.