I am surprised the mishimoto radiator is causing this issue. Glad you nailed it down to this being the root cause, but dang. I had portrayed that brand to be king of the hill for aftermarket/ performance coolers.
Me too
I bought last spring there intercooler installed it and headed to moab and loved it egts dropped about 200 degrees
2 weeks later headed to moab and water temps ran hot changed the thermostat hoping that would fix it but ran hot all the way home after replacing everything and still no luck. We pulled the intercooler and put the stock back in and the over heating went away found out the intercooler was not letting enough air flow to the radiator i returned the intercooler but mishimoto would only give me a store credit thats how i ended up with there radiator and trans cooler