When I overhauled mine I found the heater radiator almost completely blocked with dust/dirt/leaves. I would look there first. I am assuming you have a fan that works.
KA7TLT - TLCA 13015
"78" FJ-40 - "Marmot" F&R ARB Lockers, OME Suspension, MAF Shackle Rev Kit, 4+ Flip Kit, Rear Disc Brakes, Warn Winch, Safari Snorkel, 4+ Rear bumper/Tire Carrier
"95" FZJ-80 - "White Top" F&R ARB Lockers, Slee F&R Bumper & Sliders, Warn Winch, 35s, Safari Snorkel, Low Range Gears, P/T Kit
"2016" Tundra 4X4 Crew Max, -Airstream Tow Vehicle "Daily Driver"