I had hiccups for 22 days straight this year from Reta. The doctors gave me Baclofen, Gabapentin, Chlorpromazine, Omeprazole, Pantoprazole and Metoclopramide. None of them stopped the hiccups. Baclofen paired with Gabapentin allowed me to fall asleep with hiccups, but I’d still occasionally wake up with hiccups.
One drug I wasn’t prescribed but have since purchased to have on hand is haloperidol. I’ve heard that works well for some.
Frankly, this situation sounds sketchy.
Metoclopramide can cause a raft of conditions called extrapyramidal symptoms which are movement disorders. One is tardive dyskinesia, which typically causes involuntary movements of the face and mouth but can affect the whole body. If it occurs, it tends to last a while and can be permanent. You'll trade hiccups for repetitively smacking your lips, contorting your face, blinking rapidly or for a long time, maybe involuntary limb movement, pelvic thrusting, and yes -- even involuntary movement of the diaphragm.
There is an explicit warning not to use it for longer than 12 weeks precisely for this reason. If you're going to be on retatrutide for longer, it's not sustainable. The risk is cumulative, so even if you were to structure your weight loss in 12 week stretches with some interregnum, the risks associated with metoclopramide wouldn't be reset. So even if it did work for you, it is not a solution; the drug not working is probably the best luck you've had since the hiccups started.
Haloperidol is the same overall concern, though the compounds act somewhat differently in the body. The only reason it's used for long term management of psychosis is because that conditions like schizophrenia are more dangerous than the medications.
This is why I said earlier that, if baclofen doesn't work, you should stop trying for a pharmaceutical solution. The conditions you could permanently acquire are much worse than hiccups that you can cure by stopping the drug.