Hello I have a om617 in a toyota pick up and have the om617 in it it is out of a 1983 300 td and I have 5.89 gear ratios for my axle and every time I go to the mtns it over heat and the egts get 1600 ish and I have a stock toyota radiotor now with an electric fan and I also have an aluminum 3 core radiator that I haven't put in yet because my adapter plate got all messed up so I need to get a new one so right now the truck doesn't run but I am wondering if it's going to be worth it to buy another adapter plate and try the radiator out or do you guys think I should just do a different motor? everything is fine when I run it in town it only does it going up to the mtns it also pressure tested the radiotor to see if it was a cracked head and it is fine.

here is a picture of the truck let me know what you guys think thanks for your time.