Yeah, I hate to say it, but you got a rod about ready to go out the side of your block.
You need to overhaul the engine and replace the wrist pins or put a good used engine in there.
You can get a good used 4.0 SOHC for about $750 at a salvage yard.
I guess because it would cost around $1700 to do that.
I'm all for the 5.0 swap but it cost a lot of money and you really need to have a doner Explorer unless you buy all the accessories with the 5.0 and that can be a nightmare.
Start by checking if any of the plugs have backed out, but if I were a betting man my money would be on the bottom end of your motor. Rod, piston, or bearing would be a very good guess. Whatever it ends up being is going to cost you some major bucks.