Replacing engine computer

Level of difficulty is simple, no special tools, the only thing is just like with your home computer be ware of static electricity.

Location if you don't already know is left side front of engine compartment.

I'm going to break this down b/c I don't see your problems being related. I'm assuming the "liftgate open" light problem is intermitent. I would try liberally spraying the latch assemblies down with some type of spray lubricant and working the hatch and doors a few times. The ajar switches are inside the doors attached to the latches and are prone to sticking. I don't recomend using WD-40 or any other type of "rust breaker" for this. They are corrosive and can make the problem worse.
On your door locks. My thought is you have a lock/unlock switch that is defective and from body vibration may be trying to lock itself. As a rule, these switches are pretty sensitive.
Your performance issue. You can have a shop hook the vehicle up to a perfornance diagnostic unit, but I think you'll find it's just the "nature of the beast". They are not known for excessive horsepower. Hope this helps.

It could be eather one or both or even one of the grounds on the jeep check all the grounds mostly the one under jeep that goes from frame to the exhaust to the trans this is one wire that goes to all 3 but would like to know code for check engine

Here is the location on the PCM engine control module in the diagrams below that also explain how to replace it. Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

Is the engine light on again? If so is it the same code? Are you up to testing a couple of things? Did you replace the fuel filter too? You replaced plugs and wires correct? You will need a digital multi meter to run some test ok.

I think I would start with the fuel filter it just infront of the gas tank. P0171 is lean condition bank 1 and this can be a lack of fuel by having a plugged fuel filter so thats why I say start there and you have never replaced it so it won't hurt to do it anyway and eliminate that as the cause ok. Once that is done see how it runs and let me know and we will go from there.

You have a standard cherokee or grand? On the grand cherokee it is just infront of the tank as I have 99 grand cherokee, on the standard cherokee it don't have an inline filter. With that yes it could be an o2 sensor. You don't have any vacuum leaks do you? If not then I will walk you though on testing the o2 if you want.

A used one is a bad idea if your vehicle does not have the factory anti-theft system. If it does, you can use any computer. If the one you get isn't programmed for anti-theft, it will learn that from the Body Computer the first time you turn on the ignition switch, then work normally. If your vehicle doesn't have it but the used computer you get does, it will teach that programming to the Body Computer. At that point the engine won't start because both computers will be waiting for a disarm signal that is never coming. At that point you will need to replace both computers at the same time with ones without anti-theft programming.

You are really rolling the dice there. Just because it came out of a 97 doesn't mean it's even the right one for your truck and it definitely has to be programmed before use.