So my 99 Taco 3.4 Auto. Ever since i purchased it I would easily rise the temps climbing hills. But Slightly progressively over the past 2 years the temps would rise greater over hills. As of tonight driving from Los Angeles to Barstow which includes one large hill but mostly a even flat drive the truck was at above average temps of about 203-210 F. The only way i made it this drive or any other time my truck wanted to overheat "usually temps of 212-220 above" is by keeping the rpms really high or turning on the heater which did help significantly. And when I would come to a stop the temps would raise agian somewhat quickly. Im stumped is that the radiator was just replaced with a dual core, replaced oem thermostat, waterpump , and change the radiator fluid. Im guessing the fan clutch is suspect, the head gasket , but I just did an oil change yesterday and the oil was fine. And I do have an aftermarket bumper with a skidplate which blocks some airflow and I removed it and it helped but it still raises the temps.