If I were closer, I would personally
come over and look it over and try to help you sort it out. Unfortunately, you are to far away, me being in Florida. The first thing you need to do is get good tires on the car if you have not done that yet. My second suggestion since no one close by has volunteered (yet), and even tho funds are low, is still call the closest GM dealer (service department, preferably perhaps the service manager), that can service your car and explain what happened to you, what the car is doing and that if there is any way they can help you get your car running normally. (don't tell them tho that the cat was flamed, must be an old trick or something) Let them make some suggestions, and approximate costs, including a flat bed to take to car to them if you can't drive it, the worse that can happen is you say no.. On the other hand, you just might find a good person willing to assist you, AND maybe
provide you a decent discount for the parts and labor, even perhaps the CAT under warranty. If you feel that they are taking advantage, or you don't feel right, have a friend with you to help, a male friend that you trust, heck it can also be a female friend, you would be surprised how many women mechanics, or women that know cars, they can be tuff negotiators too (like my wife)
.. Also you can always try more than one GM dealer if available.
Obviously the car is experiencing a multiple problems, some obviously related to what that scoundrel you were dating did, and also perhaps a delayed problem that he might of pushed over the edge with all the tampering he did to the car, leaking fuel is not a good thing, the fuel tank and fuel pump is located in the truck, the AH might of punched a hole in the fuel tank, it would need to be thoroughly inspected. The CAT I think has a limited warranty, I want to say 8 or 10 years or 100,000 miles, unless it was tampered with, you stated that some dude flamed the sucker, to me it sounds like it needs replacing.. These issues could be simple, or complicated and expensive. The only way to get a handle on this is at a minimum take it to a GM dealer for a thorough inspection, even if you do nothing else, they might be able to at least getting running safely, and cheaply (if that is possible).. BTW, don't let one low life keep you from dating, not all Canadian men are animals.. A good one is always around, just got to find each other...Stay safe!!