Jeep reverse problems and grinding problems

USA CAR, LHD , LEFT HAND DRIVE CAR NOT OUR EXPORT.
A/T BOX.
STUCK IN PARK MEANS THE LEVER DOES NOT MOVE
no you mean, PRNDL, R D and L are all dead,
but the shifter does no jam up ever.

GRINDS, NO GOOD A/T BOX GRINDS EVER.
I HAVE JEEP MANUALS, MOST.
1ST YEAR COMMANDER, AND IS near same as grand Cherokee in regards to the trans mission, but 2 kids are used.
no VIN posted so I can'T know what is under the hood and behind THE ENGine.
3.7L or 4.7L??? GAS ENGINE or the Diesel>??
2wd or 4wd.
NAG1 OR 454RFE.
DIY
check all fuse first
then scan the cars DLC OBD2 port (16p) for errors called DLC
codes,
if it tells you shift solenoids are bad, then you know what to do next

or the cables under the shift lever box to transmission are rusted and snapped off.
the shift lever must go to DRIVE then below on the actual side of the transmission, the lever there must go to the detent DRIVE
or it fails hard.
quote
The floor shifter lever and gate positions should be in alignment with all transmission PARK, NEUTRAL, and gear detent positions.

Sounds like your synchronizors are shot. Try double pumping the clutch. May be time for a rebuild.

Did you check your ATF level? I have an ATF leak somewhere and when my ATF gets really low my auto trans will keep slipping out of gear until I dump another quart or two of ATF fluid into the trans.

Give a try by change your transmission/filters and Transfer case oil.

Problem is likely either a worn shift fork or bad synchro (both inside the transmission) It's unlikely that you have a clutch problem otherwise the problem would be with first and reverse and shifting other gears would also be difficult.

If you can select another gear with no grinding and clutch feels normal likely either the reverse synchro is worn out or an internal shift fork is worn...either way, trans needs to come out and be opened up to check. Can you put it into reverse with the engine off?

4L is for ice or dirt only.
here is the wiki on this boxc

In 1996 the NP249 was replaced with the New Venture Gear NV249 transfer case. This added a mechanical differential lock to 4WD Low mode, making it much more durable for serious off-road use.

stay out of 4low (unless serious off road)

if this is a 5 speed manual transmission...all you need to do before putting your jeep into reverese is puting it into first gear and then shifting it to reverse to avoid any grinding or problems shifting into reverse...this isn't a problem just a poor jeep design by not installing an extra gear to eliminate this grinding or shifting problem

Take it back to the guy that did the work. Sounds like he's got the pressure plate on crooked putting it in a bind. Whatever it is happened during the installation. That's a given!

Make sure you have enough fluid, and honestly, regardless of the fluid level, change it and put in new transmission fluid. If it's an automatic, change the transmission filter too. You can try adding some Lucas stabilizer as well. If that doesn't do it, you may be looking at a rebuild or replacement.