Late this spring I purchased a 2019 725DT6 with a rear discharge deck with 570 hours on it from a dealer. The mower was a trade that had come from a local municipal purchase. Usually these are taken care of well so I agreed to an as is purchase after testing it in their yard for a bit. Had a few issues that I have been able to resolve, but one that has been a problem since day 1 has me perplexed. The drive motors operate very quiet and as expected, until I get on long runs then make a turn. The motors get loud and start slipping on both sides after the turn until I move about 25 - 30 feet then it stabilizes and runs OK until the next turn. The expansion tank is about half full cold and about 3/4 to 7/8 hot, though it was low when I purchased it. These are self priming as I understand it so there should not be air in it anywhere. Though not required for another 400 hours I was going to change out the fluid and filter to be certain a dirty filter is not the problem, but before I do that thought I would ask the question here. Has anyone run into this problem before? Any ideas? Thanks.