Although the car has shown promising dry-weather pace, it has not been so strong in the mixed conditions that have been a feature of testing.
F1 rookie Gutierrez believes using the Pirelli intermediates is the C32's current weakness.
"We did work on the set-up considering we are struggling a little bit with the intermediate tyres," he said after the first day of the final Barcelona pre-season test.
"We did our best and I think it was a very useful time to work on that, but that is our weak point. We are just struggling to make temperature in the tyres."
The more experienced Hulkenberg, who took over on day two, played down the issue, but did concede there was work to be done.
"I think the [low track] temperature plays a role into that as well," he said when asked by AUTOSPORT about the problem.
"I didn't really do a timed lap on the full wets [for comparison] - I felt at no point was it wet enough to put them on - but the intermediate needs some work.
"We need to understand and get it going."
Hulkenberg also confirmed that the C32's Melbourne specification would be determined on day three at Barcelona.
"From then onwards we will pretty much know the [Melbourne] spec," he added.
"There's always room for improvement everywhere. As I have said before, I think we can still work on the low-speed performance."