I had a 6' belly deck on my JD. Also had a loader,rota tiller rear mount,grader blade for the rear and a box grader.
Depending on the size tractor. JD has a belly deck you can drive over to mount and un mount. Makes it simple to do. My old one did not have that feature.
Been some time that I drove the W20.
Thought the MPH was hire than 55.
To the OP. Reason we mention this. Engine is working harder in 4th than in 5th.
Trans also.. Many coach builders did not allow for good engine air flow also.