My 1993 discovery v8 auto wont change into 4th gear

check for broken cable or clutch fluid loss, if fluid is low top up with brake fluid and bleed any air.

Hi welcome main problems are the abs valves causing the 3 dash lights (search 3 amigos online) a really badly sited compressor can cause air suspension models to fail giving the bags a slow leak the V8 is a solid engine but can have radiator expansion tank and cap failures
the other issue is electrics windows and door looms are problematic

A misfire feels like the engine is studdering, is that what it does? If it is a misfire you will also have a blinking check engine light when it occurs.

bad news you'll need to have your tranny replace or overhauled

Have a 99 disco....I had to take the gear selection control box, underneath the center consol. There isa switch that came loose that interfaces with the brake and ignition to start the car. Also there is a selenoid in the box that could go bad. also could be a bad brake switch. Try pushing the gear shift foward in park while cranking, if it cranks then the gear selection switch is bad. The problem is between the key switch and the starter....trace it down. Also you can buy cheap a LR repair disc.

This is likely a faulty pump unit. When they get worn internally they tend to "froth" or airate the fluid. Could you see where the fluid was leaking from?

yes u can do that/ thats where u actually refil the auto transmission with fresh ATF

This is a very common problem which can be fixed for under $100 without removing the transmission

It is the end clutch which can be removed as an assymble aout the side of the transmission. New parts will run under a hundred. Serch and you will find pages that show pictorials on this repair.

If disco is automatic move the transfer lever from high to low box and back again firmly then the key will come out there is a safety feature on the autos to prevent the key being removed if the transfer box is not in either high or low correctly with most dicso;s the transfer shift lever is stiff. through lack of use .once it is pushed in properly the key will release it works every time and I have had four v8 autos
basically you cant remove the key because even though the gearbox is in park if the transfer gears are not fully home the park sensor on the gearbox thinks it is out of gear eg not in park so wont let you remove the key and leave the car out of gear in case it rolls away .Dan

Have you checked the High-Low ratio lever.  Half-way between High and Low is a Neutral, so no drive to any axle even if a gear in the main box is selected.
Try locking the differential.  If this gives you drive, then it might be a final drive (half-shaft) failure.