Good comment Plazbot.
As one who loses a night's sleep each week (transatlantic), I know just how exhausted one feels around 06-08 when landing. To be truthful, it feels like being pissed, and I certainly slur sometimes on the R/T. And yes, readbacks are tricky. This happens after weeks of no booze at all, just a fatiguing job. And it is the same for the younger pilots, some of who seem to need more sleep!