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It's been an up-and-down start to the season for Fullwood, who began his 2021 campaign with a fifth place finish in Race 1 at the Mount Panorama 500.
He followed that up with 13th in Race 2 at The Mountain, but struggled in changeable conditions at the latest event, the Sandown SuperSprint.
Speaking with Speedcafe.com, Fullwood said the team is working hard to understand its new set-up.
“The biggest thing obviously is we've just changed our package over the off-season, so we've got to re-learn it again,” Fullwood explained.
“We're making some big swings to try and work it out. We've been a little bit hot and cold with it. We've been feeling it out.”
Fullwood claimed finishes of 24th, 15th, and 13th at Sandown International Motor Raceway in a weekend where both he and team-mate Mostert said they wished they could have started again.
While it was a tough time for Fullwood, there were some smiles on the other side of the garage as Mostert put the #25 entry on pole position for the first race at Sandown.
Mostert would go on to claim sixth in that race, fourth in the second outing, and 24th in the finale after a throttle issue.
“I think the package is good and I think when we work it out and hit the nail on the head, I think it'll be a fast car,” Fullwood added.
“Chazzie obviously showed that with a pole position. He did an amazing job all weekend. Just didn't quite fall our way as a team. That's just how it works sometimes.”
While Fullwood wouldn't detail exactly what the team had changed, he noted that tools the team had previously used were having a different effect on the current set-up.
“We've just changed components in the car and it just changes how the car handles a lot,” said Fullwood.
“As a driver, you have to regain confidence in that. Some of the old tuning tools we used to go to don't work any more and they react differently.
“You kind of start from zero a little bit. We're getting there.”
Despite a tough showing in Sandown that saw Fullwood slip from seventh to 12th in the drivers' championship, the Darwin driver is optimistic about the forthcoming round.
Supercars will head to the Apple Isle next month for the Beaurepaires Tasmania SuperSprint where once again the championship will have three races.
“I worked a lot on braking this round, which is a strong point for me,” said Fullwood.
“I'm excited to go there and try and put a big emphasis on that. It's super important at that track. I don't see a reason why we can't be fast there.
“Whilst we didn't have the best weekend [in Sandown], there's still information to look into for us to debrief and try and work out what things we can do better.
“I think if I was able to hit the reset button and go again this weekend, I think it would have been a very different weekend, but sometimes you've just got to roll with the punches and do the best with what you've got.”