Steve, no warning signs yet, the truck has 90,000 miles on it and everything seems fine. But I pull fairly heavy loads at times, and to reduce the possibility of a 5th gear problem I usually use 4th. , especially if on local 2 lane roads. However, at times I need to get on down the road a few hundred miles so of course I make use of 5th.
From the experences of others, higher than stock horsepower + heavy loads = 5th gear failure. I do expect it to happen, so I'm gonna go in on a preemptive strike and change the nut and stake it several times.
Greg, yes you can repair with the trans in the truck by pulling the tailshaft housing, but you have to remove the transfer case on a 4x4.
RJR