You need to provide more detail.
I cannot directly answer your question, but there were several transmissions in that tractor. Ranging from 3.6MPH in 5th up to 8mph in 5th gear. BIG difference. So for starters, what transmission do you have.
Second, how big is the harrow.
Third, what kind of power are you "used" to
Fourth, how does the tractor run otherwise? Gas or diesel? Any smoke? does it sound normal? start okay or need ether??
Fifth....you get the idea. We need more details. I cannot directly help with the problem, as I dont have a 3000 of any kind. But there isnt anyone who can help without knowing these questions I just asked.