While trying to drive out from a slippery off road turnaround spot, became mildly stuck. After being towed out, engine would not turn over, only solenoid would click. Battery is fine. On further examination, discovered that engine is seized. Suspecting broken timing chain, removed valve cover. Timing chain and guides appear just fine. Put wrench on large top chain sprocket, and mild pressure will move nothing. 289,000 miles, plenty of oil. How to determine if cam or crankshaft is what is seized. How about lower end of timing chain?
Or do we just junk it? Has been running fine up to this point. Doesn't burn oil.

Try turning the crank pulley (it's a big socket, and remove the spark plugs first to relieve the compression).

Those trucks are bulletproof, and a new KA engine is a hell of a lot cheaper than replacing the truck.

p.s. Welcome aboard, Bill!

Thanks for the info. I'm not with the truck at the moment, so I am not looking under the hood. I assume that I can get a metric socket on the crank pulley without removing a bunch of stuff? Another strange coincidence: On examination after it was towed in, the alternator belt was lying there broken and semi shredded. What was that all about? Why should that have anything to do with "seize up"?

How about the possibility that the alt belt jammed up under the drive pulley and has it locked up> That was my first impression, but some "mechanic" gave a quick look and said "the engine's seized"

Think you just might be on to something.