Jeep - Liberty :: 2007 - Dies After An Hour On The Road - CEL Comes On?

My dad has a Jeep Liberty that has been having some trouble while on the road. It's a 2007 and it's got close to 300,000 miles on it. Now, I'm not great with cars - I can change a tire and probably tell you how my oil looks, but even I know 300,000 is a solid amount of mileage for any car to have. A while ago, the Liberty broke down while my dad was out and he had to have it towed to the mechanic. Mechanic said he thought a plate within the battery had shifted and so he replaced the battery. Not long after that, the car died on my dad again. He describes the car as going haywire right before he has to pull over. Indicator lights starting going on, dials (such as the tachometer) would jump back and forth and the engine would rev without hitting the accelerator. And after he stops the car, it doesn't start up again.

When my dad was able to get it back to the mechanic after that second instance, the mechanic said he thought the Electronic Control Unit (ECU?) might have been fried by the battery and had it sent to the dealer to have the unit replaced. They replaced the control unit and the car ran for a while, but sure enough while my dad was out one day, the check engine light came on and it appeared that the car was once again going to freak out and die on him. He was able to make it back home, yet the car has been sitting in the driveway ever since. I turned the Liberty on today and just moved it around the driveway and I noticed the check engine light is still on and a "Part-Time" indicator light that is on, but flickered while I had the car running.

From what I understand, the Check Engine light has been perpetually lit at many times during the life of the car even after tune-ups and inspections. Could this be an electrical problem or mechanical? My dad thinks it might have something to do with the transmission, since it has been replaced before. Now, my dad and I are both aware that the Liberty is close to being laid to rest, but we also both think that it's still got some life in it worth trying to save. I had a problem with my motorcycle that seemed similar to this problem, between the haywire tachometer, the engine revving without hitting the gas, and not starting up after stopping the engine. Turned out that it was a short that caused that problem and it was quickly fixed by a mechanic. I know that does not mean it will be the same diagnosis, but that is what the Liberty problem sounds like to me.