Overheating Problems

[Aussie Surfer]

I own a 92 model Hilux Surf with the 2.4 turbo diesel. The problem I am having is that under load the temperature starts to creep past the half way mark. Once was through some soft sand for about 10 mins and the other up a steep gravel track for about 10 mins. This is happening in high range 4wd. I have installed an electric thermo fan to the front of the radiator which is wired to run constantly along with the original belt driven fan. The head has already been replaced and I'm not keen to do it again. Hopefully somebody knows a solution to keeping engine temps down

Thanks in advance