It sounds like you covered a lot of things, that's a pressure cap usually their rated to 16 psi. One thing I've run into with those gen 3, 4 engines with high mileage is that little steam pipe (3mm/ 1/8" l.D. so it doesn't take to plug them)that's connected to both front area of the cylinder heads gets plugged along the coolant reservoir inlet where pipe feeds into it creates basically a big steam bubble that can't purge from the engine into the reservoir which can cause a restriction in the inlet flow and that steam can't purge through the thermostat being it's located in the bottom hose. Another issue I've seen (not that common) is being how the cooling system is designed (reverse flow) the small passages in the head gaskets (there progressive, small to large being there's no cyl.head crossover)towards the front of the engine get restricted or plugged reducing coolant flow. From the head to the block. Worst case would be to remove the cylinder heads and manually clean out those passages and of course replace the head gaskets.When you replaced the water pump it's recommended to do power flush in order to rid the cooling system of any possible debris that may cause blockage. Bottom up and top down. One other issue I've seen is that tranny can be running hotter than normal (normal tranny temp is around 180-220° when trannies run hot it's usually caused by internal slippage.) being where the cooler is located in the radiator (engine inlet side or radiator outlet) it basically reheats the coolant going back into the engine. Do mean to ramble on, but those are some of issues I've run into when l was a mechanic.

Great video! Good job and thanks.