Have you done a compression test, vaccumm test or a leak down test?
this will tell you the condition of the top end and if you have a blown
head gasket. Any water in oil? Is it milky, and smoke coming form
exhust? Any visible leaks underneath the car? Water pump working
(Not leaking or the bearing is not making a whinning sound) and the
themostate opening? Water jackets leaking? Any of these questions
should be considered when trying to trobleshoot an overheating problem.