Final update (finally): After 15 long hours of troubleshooting with my mechanic, leaving absolutely no stone unturned, he called it quits. I wasn't ready though. As my grandfather used to tell me "Every problem has a solution". After replacing the fuel pump 3 times, the PCM 3 times, and even a different instrument cluster, there was no resolution. With nothing to lose, I asked him to do me this one last favor. Remove that goddamn remote starter/alarm kit (that never even worked in the first place). He did, and low and behold, the Jeep is now fixed, unsurprisingly it drives way better, more smooth, with no hiccups, nothing.
I can also finally drive my Jeep without carrying a jerry can in my trunk all the time as well as get it inspected and be able to park on the side of my house without getting a ticket.
Thank you everyone for your help and patience through this adventure haha