Personally, I'm extremely skeptical that a species of mammal that large has escaped detection. When was the last time a new species of any size was discovered anywhere in the world? We're not talking about a bird, rodent or insect. If somebody could tell me when the last 8 foot long mammalian species was discovered on this planet, I'd sure like to know.
Somehow, we're to believe this has avoided being found despite legions of people looking for it -- unlike other small species that are found by accident.
As for the government concealing it, I don't see the motivation. It's not like it would offer technological advances or pose a threat through mass hysteria. Believe it or not, the government has more to do than operate a vast conspiracy to conceal knowledge of an overgrown monkey.