If you are absolutely sure that you are going to purchase a new Frontier next month, then I wouldn't worry about a new clutch. However, if it were me and there was a chance that I would be hanging on the truck I would go ahead and replace the clutch while they have everything apart, regardless of how you drive it. For example, I'm on 105,000 miles on the original clutch with no problems, but I've also seen clutches on other vehicles fry at 60,000. For me, the "peace of mind" of knowing that I had a new clutch along with the new tranny would be worth the cost of a new clutch.