Tupou kick-started his NRL season with two tries and one try assist in a man-of-the-match performance in the Roosters' 34-20 win over South Sydney at ANZ Stadium on Friday night.
"Once you play rep footy, you're always burning to get back there," said Tupou.
"I think it's probably the hardest I've worked since my first year in first grade and I'm just getting fitter and stronger.
"Since (coach Brad Fittler) took over, he's really made me focus on just the little things in my game and in my life and to make it all a lot better."
The 25-year-old's superb start to 2008 is also going to increase the interest in his future.
Tupou is off contract this season and has already fielded offers from other NRL clubs, including last season's runners-up Manly.
Coach Fittler said the Roosters would do their best to retain Tupou beyond 2008, but understood there was significant money being thrown at the five-Test player.
"We're going to do our best, but I've heard a lot of clubs are willing to pay really big money so we just have to wait and see," said Fittler.
Tupou admits he is undecided on his future, but with the Roosters predicted for premiership success in the coming years he knows it will be difficult to leave Bondi Junction.
"I'm still not sure. I feel the same as I did for the last few years. I love this club and really want to stay so much," he said.
"Things are happening here at the club, no matter what if I stay or go. I just want to be a part of it."