Clogged heater cores seem to be common in Cherokees. (from the one's I've owned and come across).
No need to take them to a shop to have them flushed. It's easy.
Your core will not get properly flushed using a normal flush fill kit. If its clogged the flow will just go elsewhere and not thru the heater core.
To flush only the core, try this.
Disconnect both the lines to the heater core at the water pump and thermostat (easier to get at the connections at the front of the engine and it gives you a couple feet of hose to work with).
Take your garden hose, no nozzle connected just the end of the hose and turn it on medium flow.
Wear clothes you don't mind getting wet, and do this in an area that has plenty of space/drainage.
Hold one hose over the edge or the car (having a friend around helps) this will be the outlet. Using both hands, push the garden hose against the other heater hose and seal it with the other hand. Water will spray from your hands, don't worry about it.
The water pressure from the hose will flush the core. Hold it for a few seconds, then pull the hose away and repeat several times. This on/off cylce causes air to get in and helps the flushing process as does the surges of water when you do this on/off thing.
You will get 'bursts' of nasty stuff that flow from the heater core.
Now, reverse the flow by flowing water into the other heater hose.
Keep doing this until no more nasty stuff comes out of the core. It take me about 15 minutes to do this. (20 or more gallons of water). You can turn the hose flow up after the flow thru the core is decent. If you start with too much flow from the hose too quickly it just sprays you down more.
You should notice a considerable increase in the flow thru the core when finished, in comparison to the flow when you started.
Note if you have a valve in you heater lines, it will need to be open for this process. I use a zip tie to hold it open. Or best is to remove it and go directly to the heater core with your hose. But this makes a bigger mess and can drown the inside of you vehicle.
I did this in Colorado after commuting over the moutains in winter w/o heat for a few weeks. Had to wear a jacket and snow shoes inside the car on the way to Telluride every day.
Flushed it and it was all warm and toasty from then on.
Good luck and let the heat flow!