Gloucestershire finished their first innings on 463 thanks to a century from Ryan Higgins, before injury to skipper Cooke hindered Glamorgan late in the day as he was forced to retire hurt on 23*.
Glamorgan ended the day on 241/8, with head coach Matt Maynard honest about his team's performance during the course of the day's play.
"I think we've been off the beat in the whole game," said Maynard. "Our fielding's not been up to standards that we set during the first game of the season and during the Royal London One-Day Cup. We've been a bit sloppy in the first two days compared to the standards we've set and that we want to reach."
"We have an opportunity to turn it around in the next two days, to reach the levels we want to try reach more consistently. We'll aim to turn it around in the next couple of days and get something out of this game."