I feel your pain! My gun dog has been far harder to train with recall than previous dogs. A few months ago I thought I'd never be able to let him off. But now we're making massive progress. My trainer said we have to make him see there's more value in coming back to me than leaving me. Sounds like you're doing all the right things, with tasty high value treats. Cheese works best for my dog.
I was told to go back several stages. Start in the house/garden, which he was already good at. But interrupt him while playing in the house with a recall command. Then throw him a treat on the floor, let him have it, then call him back and give him 5 treats, so the value in returning to you is greater.
Repeat with other distractions. Like someone calling him to the top of the garden. You can him back and treat heavily.
Keep repeating in garden/ house. Then go to a quiet outdoor area. A car park after closing time, etc, where there are limited distractions. Have him on a short lead. Let him sniff around. Then call him to you. Treat heavily. Repeat somewhere safe but quiet and boring, on a longer line.
Then when you are confident, go back to the field on a long line. Then eventually.... off lead. It's taken 6 months and he pretty much comes back to me instantly now. 8/10 times 🤣🙈
I've taught him an emergency stop command too. So if I shout stop! He stops dead. (7/10 times 🙈) We have a lot of bikes etc, so this was useful.
Good luck! It's been a hard slog, but 100% worth it. We enjoy our walks now. They were torture 5 months ago. My dog is also 1 x