1986 Toyota 4x4 Manual transmission

The wife took the truck out on the highway and said that she couldn't get up to 65mph in 5th gear. Dropped down into 4th and got back up to 65. When she got to some real small hills, she lost power but the engine reved up when she hit the gas. She slowed down to turn around at an approach on the road and one she stopped, the pickup wouldn't move. It reved up fine. Shifted between gears fine but wouldn't move. Once the truck was towed home, I looked underneath and there is some fluid around the transmission case where the drive shaft attaches. I had her hit the gas and let out the clutch and the drive shaft turned approx 1/8 revolution. The engine sound fine, It didn't stall at all, She said she didn't hear any clunking noises. She said that it just started losing power until it eventually wouldn't move anymore. Any suggestions as to what could be the problem?