ISX High Oil Temp

[JCTL Jamie]

Have a 05 KW quad Dump truck with an ISX. Been having a stop engine issues here as of month or so, last week took it to the shop to get the computer hooked up. It said the fuel pressure at low idle was around 240 and at high 280 said causes of that one would be the fuel pressure sensors. I changed the 2 of them this weekend. The issue happens when loaded and generally pulling a hill although it has happened one time empty it was a long highway ride at higher speed which for the gearing in this truck is around 67. Ran good most of the day but last load sure enough red stop light engine I forgot to say soon as you pull over and stop it will go out sometimes for a couple hours sometimes for a min. Take it right to the shop no fuel pressure codes, does have oil temp higher then normal operating range it says causes low oil level I just changed it this past weekend so doubt that one oil temp thermostat or oil cooler. He did run the truck at high idle for around 5 min coolant temp stayed about 184+- oil temp started at 220 within the 5 min was at 239 Is it worth replacing the thermostat or should the whole cooler be replaced? anyone ever have an issue like this. what do y'all think

thanks
jamie