Light rod knock in a Durango 5.9... is it terminal?

I'm gonna leave the engine alone and just put some additive in the oil to thicken it up. I only filled it with Valvoline Synthetic 10W-30 so I know it can go thicker, I think I'll drain a quart (in a clean container then put it through a coffee filter for reuse) and add back in some STP mixed with some Mobil 1 15W-50 I have.

While waiting for the water to drain on the final cooling system flush (original issue was a cracked radiator) I checked the trans fluid; the color was ok, slightly brown/gray but no real smell at all. I am making money off doing all this work so I'm not trying to cheap out and do the least required work, I want to actually get the whole car solid so she can go tell all her friends how I magically made her car drive like new again :D plus more work = more money. @TrailBeast I know it was probably a joke but like I said this thing was a basketcase when she brought it to me and she was fully aware she had neglected the maintenance badly so I highly doubt she'd blame any future problems on me. I saved her from being screwed over by a local shop that wanted to charge her $1000+ to fix her cooling system and do some other random BS that isn't even needed.

Most likely tomorrow evening I'll go under and adjust the front band on the transmission, if it brings back 2nd gear I'll ask her if she wants me to drop the pan and change the fluid and filter. I'm tempted to try an at-home flush as well using this method (it's even the same transmission in this video lol).