You will see more improvement from riding with a faster group. You want a group that drops you a little on every hill. Just don't get discouraged. Keep after them. Try to pour it on, right as you go over the top, and then hold a fast pace. Probably they will slow a good bit to recover. You don't, just keep after them. You'll usually get them back. Ride 'til the blood comes from your eyes and you see bits of lung on your shoes. After a few weeks, some might even have a little pity and wait for you, but don't count on it.
Keep food where you can get at it. Pre-tear your bar wrappers if you are using bars. Or use Hammer Gel and take a couple of their flasks with you. I much prefer that to sticky gel wrappers. It has to be easy or you won't do it.