The Durban side garnered an impressive 39-27 victory over the Blue Bulls over the weekend - their second over their Pretoria rivals in the season.
"We still feel we've got a lot to do," he said.
"We’re still seeking that game that we really want to play and saw good touches last week which was great, but we're not quite there yet."
Plumtree was particularly concerned by the work rate of his defence, and for a second week running, highlighted the importance of refining that area as they prepare for the Pumas at King's Park this Saturday.
"There are so many areas of our game that are good but we made 208 tackles against the Bulls last week and they made 70," said Plumtree.
"So physically, we know if we don't turn that around by the end of the Currie Cup we could be wearing ourselves out a bit.
"We'd like to get a little bit more discipline with what we’re doing in attack and got a little bit going last week.
"Obviously we were quite dangerous with turnover ball and some of the tries we scored last week were really good."
Bad news for the Sharks was Charl McLeod being ruled out this week because of a shoulder problem, though, Eugene van Staden (elbow) and Jean Deysel (thigh) are expected to be fit despite the latter sitting out Tuesday's training.
Plumtree's men are well placed for a home semi-final with four of their remaining six games in Durban, including visits from second-placed Western Province and log leaders, the Golden Lions.
Their problems this season has come against the lesser unions, and just pipped the Pumas in the first game in Nelspruit, while they struggled at home to the Leopards before losing to Griquas.
"It's really up to the players now, we haven’t talked about it at all this week," Plumtree said.
"They’re growing as a group, hopefully they’ll show some maturity and respect for the opposition and come with the right attitude."