These problems can be really tough and frustrating. At highway speed, say 50-60 mph, you should be getting enough airflow through the radiator core, and should not have an overheating problem, even with no fans. Right or wrong, this is what I would try. Get to highway speed while the engine is still cool and see what happens. The temperature should raise to no more than 160 or so while you are at speed, then rise rapidly when you slow down or stop. If the temperature stays down at highway speed, the radiator and engine coolant flow are probably OK, and your problem is likely fan related. But, if the temperature keeps rising at highway speed, I would then try checking the coolant flow through the radiator and from the top radiator hose. If you are not already running plain water, drain and save the coolant, because otherwise it will get all over everything and can be very hard to get off. With no thermostat installed, I would disconnect the upper radiator hose at the radiator and watch the flow. Tape off the radiator upper hose input, stuff a garden water hose in the radiator filler hole, turn on the engine and the water, and look for a strong flow. If the flow is good, water will spew out. If the flow is low, then you can start troubleshooting. If the flow is good, I would suspect the radiator. Checking the flow is very messy, so if you can think of a way to capture the water please tell me how you did it.