My sympathies too. (Am now so nostalgic for the days when I had a lab trundling 4 paces behind me at all times.)
What I can't figure out is: you're not supposed to keep shouting or whistling for them to come back as it becomes background noise. But how long are you supposed to wait (panicking) before you whistle again?
Often wondered about this myself

I've always taken the view that once they're
out of sight lost

, it's best to keep calling regularly. But I don't do it if they can see me, I always try and catch them on the return - makes me feel good, makes them feel good, we're all happy

.
He did make me laugh the other night though. We'd been yelling, at dusk in the forest for him for about 25 mins. Normy who's usually pretty good at finding him was fed up and refusing to go and look for him and huffing quite a lot so OH and I were about to split up and take separate paths to give us a better chance of finding him. When suddenly, he appeared

. There he was charging up the path to me, tongue flying in the wind white flag tail in the low spoiler position, running back to me as fast as his little legs would carry him. My heart melted and I armed myself with a handful of treats, arms out to him, praising his socks off...........
but he ran straight past me and off up another path at high speed - it was as if we didn't even exist. It was only sheer luck that we'd seen him as the scent trail he was following just happened to take him past us

15 minutes later he did rejoin us but by then, my heart was firmly unmelted and treats very much back in my pocket

You have my utmost sympathy. Hunting is my one real problem with the dogs. Recall is otherwise spot on but the minute they catch a whiff off a bunny/squirrel/deer etc I'm stuffed and no amount of livercake helps. Krumble and Arwen dash off for no more than a few minutes so they dont bother me too much but I've been losing Lyra for anything up to 40 minutes so she spends a lot of time on lead and Ive just invested in a bell for her collar so I can at least hear where she is 
SO feel for you, she sounds very like Normy was.. if it's any consolation at 4.5 years old (and quite a few more grey hairs for me) Normy is now brilliant and only occasionally disappears for 5 mins max and as I've only had her two years, with any luck Lyra will settle before that age. I'll keep everything crossed for you that she does anyway

Hannah xxx