1994 Acura Legend Engine Temp Starts Rise On Hwy Start Grade Turn Heater Drops

check thermastat sounds if sticking feel hoses to radiator both should be about same temp radiador could be clogged if you got a non contact thermometer see if temp thru out radiator is same temp if different reading radiator is clogged replace check hoses to see if soft old hoses collapse and as you give it more gas they strain and cut off ciculation they should be replaced once a year and are you losing any antifreeze

I believe the cooling efficiency is p[oor and since problem occurs at high speed driving, apart from a partially stuck thermostat, you need to have the radiator checked. It most probably is partially clogged.