Could be the clutch is fried or the slipper clutch is cooked. Running in water/tall grass tends to put a real hurt on clutch shoes, be it the slipper or the shoes in the bell. Or the slipper nut just backed off.
A quick test you can do is get it up to running temp, hold the truck down on the ground and punch the throttle a few times to see where the spinning stops. If it's the engine clutch, the bell won't spin. If it's the slipper, the spur will spin, but the shaft it's on and trans won't. If it's the OWB in the trans, then the input shaft will spin, but the output won't. Just kind of have to work your way through to see what spins when under power and what doesn't. You don't want to hold the throttle long, just hard enough and long enough to see where the power is lost. Then shut it down and fix it.