The stock reached $600.01 just after the market opened but closed at $585.56, down $4.02 for the day.
Apple is the world's most valuable company, with a market capitalization of nearly $555 billion. It topped $500 billion for the first time in late February, a market value peak where few companies have ventured.
Anticipation is high for Apple's latest creation. Some industry experts believe the Cupertino, California, company could sell 1 million of the new iPad on Friday, when it becomes available to the public. Apple has already stopped taking advance orders for Friday and said customers should expect a two- to three-week wait for purchases made through its online store.
There were 15.4 million iPads shipped in Apple's most recent quarter, which included the critical holiday season. That amount was more than double its iPad sales the year before.
The updated iPad will not have a new name. Upgrades include a sharper screen, driven by a faster processing chip that acts as the "brains" of the device. The new features will make the tablet computer slightly thicker and heavier than the iPad 2, because it needs a larger battery to power the high-resolution screen.
Prices aren't changing from the previous models. They will start at $499. Versions capable of accessing cellular networks will cost $629 to $829.