I am experiencng the same issue with my MaxIV and this is after the T-20 rebuild so I know its not an issue with any of the internals being damaged in the T-20. And its not the Latterals since I adjusted the plunger travel twice using the advise given here of measuring 5/16 movement, I believe its the belt tension. After a couple of try's moving forward and reverse ( which works fine as long as I dont try to turn) while attempting to turn I had my son watch the clutch belt. He noticed, when attemtping to turn the belt did not engage and instead was slipping. I am currently in the process of adding 2in rubber engine mounts replacing the 1in mounts which will tighten the belt to 1 3/4 travel.
I havent been able to complete the update, hopefully this weekend. this should fix the issue for me. Have you checked your belt tension?