What is happening is once you turn on the fan, you have air circulating around making the temperature much more even, from ceiling to floor. Because heat rise. So if you have your thermometer at, let's say, 3 ft from ground, in a 6 ft tent, the heat gets caught at the top and you cannot read it.
Here is a few tips
-forget about intractor, (except if you already have a strong extractor witch does not seems the case)
-use the intractor as extractor, always extracting air from the top as heat rises. But really, for a 5x5 you should consider a 6 inch 390cfm as minimum.
-leave a few ports open on the bottom of the tent for passive intake. Rules of thumb for passive intake is you need about 4 times more opening than the size of the extractor. Fresh colder air that naturally is closer to the floor, will rise to the top as you extract, replacing hot air by fresh air.