1995 Chevy Suburban temperatue gauge

Other Category problem
1995 Chevy Suburban Engine Size unknown Wheel Drive Type unknown Automatic 180000 miles

the engine is 5.7 liters, think it's a two wheel drive

i had a new radiator, new thermostat, new temperature switch installed and still the temperature gauge continues to go towards the overheating mark. It flucuates. And it seems when I come to a stop it is more likely to go towards overheating. While driving I can hear the water in the reserve tank boiling/popping. And when I start to move it goes back towards normal.I haven't seen any leaks. Even though i've had to add water to the radiator after driving almost half a gallon. Some of the water seems to be going into the reserve tank it stays full now instead of being at a normal level. Someone said to have a pressure test done to check for internal leaks

any suggestions are greatly appreciated