1995 camaro cooling problem

My son has a 95 3.4 and had a defective intake gasket , ran hot , water in oil . fixed that and changed new delco water pump, electric fan, fan switch, heater hoses , upper and lower hoses , thermostat, and belts. the car is in mint condition, motor runs great , no knocks and no miss. If i get on highway temp will go to red. I am losing water , no visible leaks and no water in oil , very confused. can it be a head gasket and not have a miss. loss about half a gallon. Thanks for any help. Firetruck27.

Make sure your hoses are tight, have your son rev yhe car while you watch them, it may not leak at idle but after its war and you get the pressure up it might sprout a leak.