I, Claudius is mostly Robert Graves somewhat indiscriminately mining Suetonius and some Tacitus. The chances that some of these stories are as fictional as, say, Marie Antoinette saying "Let them eat cake," are very high.
For instance, the whole notion that Augustus was a nice old man is exceedingly unlikely. Rome has done a much better job in capturing a historically probable picture of Augustus.
The notion of Livia as some diabolical, monstrous intriguer is likely influenced by misogyny.
Graves assumes that Tiberius' retirement to Greece was just a ploy in the struggle for the succession. This is improbable, first because absence has rarely been a desirable thing in court intrigues. But, second, since Tiberius retired again (to Capri) when he Emperor, it is very likely that Tiberius on some level did not want to be Emperor at all.
Graves' contrarian bent sometimes serves him well, but other times it does not. He minimizes the slaughter subsequent to the discovery of Messalina. But when Tiberius' slaughter after the discovery of Sejanus' treachery which including the poisoning of Tiberius' son (correctly, it seems) is portrayed as a horror. Personally going apeshit on people after you find out your son was murdered is more understandable than killing bunches of people because you find out your wife is a slut.
As Graves' crankish extremes in mythological interpretation show, he lacks judgment. There was a highly respected Senator who was a close friend of Tiberius, and even lived on Capri as well. Being highly respected, since he did not confirm the lurid stories about Tiberius, Suetonius et al. blandly explained that Tiberius (somehow) fooled him. Graves' Claudius just hints that the friend knew perfectly well what Tiberius up to (which is almost certainly true,) but that he lied. The simpler explanation, that the friend was telling the truth, that Tiberius wasn't up to grotesque sex play with children isn't even conceivable.
Inasmuch as no alleged partner of Tiberius ever had a name or parlayed the connection into money or used influence against a Senator, unlike other alleged paramours of emperors, the probablilty is that the allegations are falsehoods. The Senators hated Tiberius because of his informers (a good reason, after all,) and his stinginess with public funds (a matter of perspective.) It's like people who hate Obama convincing themselves he's a Muslim.
The numerous imperfections of Rome's history are just not in the same category, I think.