First, what size is the gas tank? Owners manual says 20, but it seems to be less than that. My research has shown that the other size would be 13 which would make more sense, but were any Cherokees sold with a 13 gallon tank instead of 20?

Second, occasionally on the freeway if you catch a bump just right the whole Jeep will start shaking. This doesn't stop till you either slow down until it stops, or you catch another bump just right. I knew of this issue when I bought it as I bought it from a co-worker. They had it fixed though, the mechanic said it was the stabilizers and he fixed it. I'm wondering if the stabilizers need work again or if there is anything else that could be causing the problem.

Thanks in advance for any help.

Possible tires need a balance check. I had some issues with vibration or wobble hitting bumps. I run 31" tires. Got them road force balanced. That improved problem. I just upgraded tierod and ends. Like night and day
or no issues now.

I'm pretty sure the gas tanks are all the standard 20, even for the different engine sizes. I couldn't imagine why they would be different. And I've also wondered if it's 20. I feel like it's closer to 18. I always fill up my XJ when the gas light is continuously on (not just on a hill), and I still put like 14.5 gallons in. It seems weird that my gas light would be on with a quarter of the tank still left. 5 gallons goes a long way

the reason I ask about the gas tank is I fill up when I hit a quarter tank on the guage, and from there till the pump shuts off is around 10 gallons every time

When my light goes on my trip meter will say 0 miles to empty and I have gone 85 miles after that before and it took 19.2 gallons. I was testing to see how low it would go and finally got scared so I filled up. Lol

I might have to do a test like that, fill a gas can with a few gallons and then run it dry before filling up

you need to check for play in your steering, ball joints and make sure your track bar is tight for that shaking. if the trackbar is the slightest bit loose it may have ovaled the hole and is causing death wobble.