You should always check the FAQ before posting. There's a whole topic on this subject.

Here is the order I would proceed to disable the cylinder deactivation (MDS) in your vehicle:  it’s also located in our cylinder deactivation sticky under FAQ that MountainManJoe referred too.  But here it goes:   (Your vehicle is also out of warranty so opens up the options.)

1.) Disable MDS using Range Technology’s MDS Manager OBD II device for Hemi’s 5.7L V8.  It’s about $200.  Range Technology is a reputable company and they started with cylinder deactivation OBD products on GM vehicles but later expanded to FCA products.

https://www.rangetechnology.com/products/mds_manager/

For some reason, the Jeep Grand Cherokee is not listed, so I would contact them and see if their device will work with your vehicle.  If it does, buy from them direct to get the latest firmware and also not to get scammed (e.g. get a clone).

2.)  Next option if Option #1 does not work out is to have a reputable performance shop just tune out (I.e. turn off) the MDS via software.  Do research in your area and see which shops have had experience doing this on the Hemis.  I don’t have a price for this but more expensive than Option #1.

3.)  Options #1 and 2 only disable via software but the actual hardware (cams and lifters) are still intact and still susceptible to fail although operating in V8 all the time now (by implementing Options #1 or 2) mitigates the issue.  Option #3 involves replacing the hardware (cams and lifters) with non-MDS ones and re-tuning the ECU but is also the priciest (easily $3,000+).  And again, you’d want only a reputable shop that has tons of experience performing these MDS-deletes doing the work.

Try those.

Can I Turn The System Off?

From the factory, no. However, issues with CD have become so prevalent that many people take their vehicle to a trusted mechanic to have their CD system deleted. It should be noted that dealerships do not offer this service and could (most likely will) void your engine warranty if you have any remaining.

Using AFM as an example again, the following engine components will need to be replaced:

• The 4 AFM lifters
• The AFM camshaft
• The ECU will need to be re-tuned

Depending on your location, this work typically runs anywhere from $2500 - $3500 parts and labor. This IS NOT a do it yourself project, even for a seasoned DIY mechanic. You must open up the engine and extreme care must be taken to not damage other internal engine components. In addition, tuning for the new parts must be completed by a professional mechanic, preferably with a dyno.

I Don't Want To Open Up My Engine. Is There Any Other Way?

Possibly. Recently some software companies have released OBD-II (On Board Diagnostics 2.0) compatible plug-in solutions that can disable the CD system by reprogramming the software coding inside the ECU. In theory, this allows the engine to run as it normally would if CD was never installed. These devices are somewhat new, so it is advisable to research the kit you are looking at to see if it has worked for others. These are FAR cheaper than going for the "official" delete option, but obviously are not as guaranteed to work as physically removing the CD hardware.

FAQ Excerpt - @Mod_Man