Friends i just finished a project, perfectly running the veh but has only one problem.
Its a lwb jimny sierra with a 2000cc toyota 2C turbo rear wheel engine with matching 5 speed auto transmission. Has original 4x4 gear and radiator that of a 1.3 jimny sierra.
The problem i am facing is that driving it below 80km/ hr speed, even with AC on, in very hot weather, the temp remains under control but after crossing the speed of 80, the temp tends to rise even more than half, even if i switch off the AC. I have already locked the clutch radiator fan and have removed the thermostat valve also. The fan already has a shield on it.
Suggestions needed.
Pic for reference.

You're running a 2.0 litre engine with a radiator designed to cope with the heat from a 1.3 litre engine - my guess would be the radiator is marginal at best.

Did removing the thermostat help or change it at all?  Lots of times removing an operational thermostat will make overheating problems worse. The thermostat slows the flow of water, otherwise it can flow through the radiator too quickly and it can’t dissipate enough heat.