The temperature of a gas grill is not constant. According to 4theGrill, a gas grill has several heat zones. The area near the middle of the grill grate reaches the highest temperature, while the temperature on the outer sections of the grate and on any upper racks is 100 to 200 degrees lower than in the middle.
The type of food grilled largely determines the temperature of the gas grill. The website Barbecue'n on the Internet dictates that you should cook fish at a medium temperature (325 to 350 degrees F), chicken and pork at a medium/hot (400 F) temperature and steak at a hot (at least 450 F) temperature.
Burners set on high that are allowed to preheat 15 to 20 minutes will get a gas grill hot enough to cook any type of food. The temperature inside the grill will range from 300 to 550 degrees, depending on the heat zone.