have you tried replacing the thermoswitch? its only 300 bucks yata sa casa. the thermoswitch controls the fans that cool the water in the radiator. maliit na plastic part thingy yun nakasaksak sa engine sa ilalim ng distributor.

i'd also return the thermostat. buy orig na lang mura lang yun. wag mo i-recta yung radiator fan. hindi sya designed for that. masunog agad yung fan motor mo.

everything else you've covered na. other things i can think of are weak fans (dalawa yun pag patay yung isa for long at naka a/c ka overheat) and vapor (air) lock. sa umaga try mo top up yung coolant before starting it. keep doing it until lagi na sya puno at hindi nagbabawas.