It seems like you should be able to (A) lug the engine down, even to a stall, or (B) spin the tires. If neither of these things are happening, and you find, or are told the drive system is fine, I would look at a broader spectrum of the rainbow than that shade of orange. I have only a few hundred hours of experience with a deisel mfwd tractor, but one of those two things always happened with mine.