2000 Jimmy 4.3 4x4 with 100k on it knocks

This truck sounds perrrrfect when cold but after fully warming up you can hear a knock but only at an idle. I can't figure out what it is. I took the belt off with the truck warm and it bangs and knocks very loud. I can move the crank a LOT back and forth. I think this is the noise but I was wondering if that is a known problem with these 4.3? Also...how do you fix it? I'm afraid to drive it so it is parked until I figure out what to do with it.
PS...I just bought it so it's not like it was knocking and I did nothing until now. I don't know how long it has knocked like this.
Rob

Tough to diagnose knocks from here, crank end play is not over .010", the balance shaft on those engines was also troublesome, but either way if the knock is in the block it's coming out and/or apart.

Probably why he sold it. If the lower intake was leaking Dex cool for some time into the motor or remote oil cooler line blew that would explain the internal noise from lack of oil or diluted oil. Might want to ask the guy that sold it and perhaps for your money back unless sold as is and you knew it had a problem.

It was the thrust bearing. Engine is out and I'm having a crank kit put in it. I bought it at an auction. It had been vandalized with a baseball bat. Guess it had other problems before they vandalized it. Oh well, it is a very nice truck.
Also, It has a problem with the fuel gauge. Is there a known problem with gas gauges on these things?
Rob