91 toyota 4 cyl truck overheats at speeds above 70mph and 10 minutes after start (thermostat opens late). Recently replaced timing chain, headgasket, thermostat and housing after oil and coolant were mixing. I flushed cooing system several times to clean out oil.
Check to see if front of radiator may be blocked with debri. If you have A/C you may have to remove radiator to be able to check. Just a guess!
I had the same situation with my Rav but no coolant showing up in the oil. My mechanic said if that were the case it would mean a cracked block.