Hard shifting from 4 wheel back to 2 wheel drive

Read off the OBD codes for clues.
Hard shift is caused by no speed sensing.

Find a local trusted transmission repair shop, they will do a preliminary diagnosis in most cases for little or no cost if you give them the job of repairing the transmission, which I think needs to be overhauled judging by the symptoms it is presenting.

Check for and cracked or broken vacuum hoses. When you have a vacuum leak. It usually causes really hard shifting or no shifting.

Could the front control arms be worn out and letting the differential shift around ?

I think the people that rebuilt it, will have to pull it back out

you can shift on the fly from 2 hi to 4 hi at any time as long as you are not under power or in other words on the gas. Hold at a steady speed or let up on gas pedal a little bit then shift, DO NOT shift truck when vehicle is speeding up or taking off. Also do not shift when wheels are spinning or when you are turning a corner. The same goes for shifting from 4 hi to 2 hi. ** Now to shift into 4 lo the truck should be stopped and put trans shift into nuetral then shift transfercase into 4 lo, and never exceed 25 mph in 4 lo position !!!!!!! To shift out of 4 lo and go to 4 hi or 2 hi stop vehicle and shift trans into nuetral then make your 4x4 shift then put trans into forward or reverse gear and VROOOOOM your on your way. Remember to NEVER and i mean NEVER shift into 4 lo while vehicle is moving forward or reverse as you will do serious damage to any and all parts of drive train. You should not run 4x4 at all unless you need to pull something where you need extra traction like a boat out of water,a stuck vehicle,or if roads are slippery, or muddy. also don't be alarmed as sometimes when in 4 wheel drive and you turn corners you will notice a binding or jerking motion, this is normal and if this is occurring i would recommend going back to 2 hi position. HAPPY TRAILS to you with the new toy. I only buy vehicles with 4x4 and have never owned a 2 wheel drive in my 31 yrs of driving. I love the idea that i have extra power and traction options when i need it,the only bad thing is your boss says " what do you mean you can't make it in,you have a 4 wheel drive!

No. Even if it did, the modulator only controls the 1-2 shift.

down the dipstick tube!!!(really)DO NOT OVERFILL...
Your audi is fitted with a fuzzy logic gearbox, it will change according to your driving style.TRY THIS,put into 1st and without touching gas pedal, let the car accelerate to top gear,stop Then using onle 1/3rd gas pedal do it again.then using 2/3rds do it again.then only using the minimum pedal req accelerate to max legal limit.(try not to use brake pedal,let the car slow down itself,until you have to)then drive as normal, it will feel like a different car.

Has this Jeep been modified at all?
It sounds like the shifter cable was reinstalled backwards.
Specifically the 4-Low "Not Climbing Well". 4-Low should give you the best torque and hill climbing ability.
Do you feel any "Binding" in the steering wheel (difficult to turn)?
Remember a Jeep uses real driveshafts and differentials to give you 4WD - you cannot engage 4WD or 4-Low on dry hard surfaces. It needs a little bit of slip between the wheels for turns.
Check you're fluids too.

the shifter cable has broke and the cable cost about $40.00