LANDROVERS are not known for overheating, thats american cars u must be getting confused with.
I had 2002 discovery for 2 years, drove almost all weeks in desert and never overheated once.
Check coolant level and any antifreeze is fine or even water. But water gets rust in radiator but give better cooling than coolant. So for testing water is good and then fill up with coolant for long time.
Check all fans main (clutch fan) and Aux for AC and overheating is working fine and cutting off from time to time.
Check thermostat or change thermostat when in doubt. Its cheap. (dont drive w/o thermostat).
If after all the above still car overheating, then ur engine head is very slightly bent due to previous overheating and need to open and face the head and change the head gasket.