Lockers are OK but limited use, Limited Slip(L/S) is what you want for full time use
Look on your drivers door "build label" then look here:
https://www.therangerstation.com/tech_library/axle_codes.shtml
There will be a code number under AXLE which will tell you if you have an OPEN rear axle or L/S
OPEN type is the standard axle in most vehicles, it means only one wheel will get power, the easiest wheel to turn gets 100% of the power
This is why if you ever get stuck only one wheel spins
L/S powers both wheels equally but allows one wheel to "slip" when going around a corner, when cornering the outside wheel needs to turn faster than the inside wheel, this is the "limited" part of Limited Slip
A Locker doesn't have this ability to "slip" when cornering which can cause one wheel to drag, which is not an issue on gravel, dirt, mud and snow, but...........can cause loss of control if you are not used to it, this is why most "lockers" will have an ON/OFF control, so you only use them in certain driving conditions then turn them OFF
For on road and off road an L/S is the better choice, IMO
A 1993 to 2009 Ranger or Mazda B-series L/S rear axle will be plug and play into your 1994 Ranger, just some wrench work
Axle Ratio is also important, the CODE above will tell you what you have now
If you have a 4x4 then you must use the same Ratios front and back, if 2WD then you can use any ratio you want
And just general heads up
You have a 4.0l OHV engine, used from 1990-2000 in Rangers
These have a weak spot in the head casting that will cause them to crack if overheated
So NEVER allow this engine to overheat, lol
Look at the hoses and replace any that look like they are cracking
Reverse heater hoses at the firewall, on ANY vehicle, this helps heater core to last longer
Replace coolant and flush system every 2 years
You have the last year of the A4LD automatic
Service it regularly
It NEEDS a 2nd trans cooler, all automatics do, best $60 you can spend on any automatic
What kills automatics is fluid temps above 200deg