Clutch/Tran? Problem

[VTesar]

June 29, I took my truck to the dealer because of a clatter when I had the truck in neutral and the clutch out. They found the clutch disc rattling and the input shaft seal leaking. Replaced the clutch disc, input shaft seal, and input seal.
Today, I started the truck, in neutral; sat there awhile; got out and headed for the house; looked back and my truck was in reverse headed up a slight incline. It stopped on a pile of rocks after going through several neighbors yards--gear shift lever still in neutral. Somehow, the transmission went into reverse. It should have rolled downhill, toward my garage, rather than going uphill since it was in neutral.
Question: Is there any risk of gear problems (safety) if I drive it 50 miles, in the mountains, to the dealer who worked on it; or do I need to have it towed?
Is it likely that they did something in the general vicinity of the clutch to cause this; or is it something else? In other words, what would cause it to go into reverse. I do place it in reverse when I shut down; but it was in neutral when I started. I had the impression that it kicked into reverse the other day; but I was sitting in it and put my foot on the brake and shifted about the same time it occurred. I assumed it was my imagination, at that time. 2003 3500 6-speed