My concern would be, will the new one single piston be matched to what is already in this engine. If not, you could end up with an engine vibration you`ll never be able to get rid of. If not set into the bore correctly, they`ll crack a ring land on the new piston, and or worse, break a ring while installing it. Maybe you`ll get lucky and they will get the piston right straight from FCA (in mexico) where these engines are made, and hopefully, the new piston will weigh the same as the other 7 pistons. Another issue that could show its ugly face, will the compression be changed within this cylinder with the fresh new piston and rings(?). At the amount of money your paying, i think i would have just bought a low mileage`d engine from a salvage parts yard, dump it in, done. My next issue i would worry about, will the monkey thats working on this original engine, chances are, its not going to be done correctly. Chances are, they`ll have the same idiot that dropped the nut into the engine, putting this truck back together. And they will slam it together, git ya out the door as fast as possible just to get rid of you. You`ve become a problem for them.
I feel for ya bro... they ****** up the engine, which the engine wasn`t broken until THEY worked on it. They are taking the easy way out, you`re gonna be stuck with the mess. I do agree with some posters here, you are the one that caused this nasty problem to escalate into this bigger problem you have now, but they made it worse by having some ******* screw it up even worse for you. They own it, they have to pay for their mistake, just the same as you are. Good luck my friend, i hope this works out.