I wonder if maybe he hit good #s overnight last night, and today is a liver-rebellion cycle? Hard to say really, but sometimes an ugly-high cycle can be from that.
He does respond ok to PZI IMO, you know that from the high doses he was on before, I think it's just a matter of finding the dose that works, without overdoing it like earlier. That said, there's nothing wrong either with trying another insulin if you aren't getting results in a reasonable timeframe.
The problem with switching is it's basically a do-over, and you may end up with an added stretch of higher #s as you build up the dose on the new insulin. If you haven't already, you might look at Angela & Blackie's SS. She tried both PZI & Lantus, and is finally getting good results now (YAY!!!). I suspect Blackie would have done fine on PZI at a higher dose, but hard to say for sure.
One benefit of Lantus is there is a clear protocol to follow, and more people on the Lantus forum than here to help walk you through it. So to my mind, those aspects make it appealing, especially when you have a kitty with atypical patterns, or confusing #s. But on the other hand there are some minuses IMO to using other insulins, and also you could basically expect several weeks of higher #s before making progress. It may be that he needs a dose like, say (just picking a # here) 4u. If that were the case, you may be close to a breakthrough on PZI, and switching insulins would put you back at a lower dose & building back up.
If it were me, I would probably post on Health and ask for eyes on the SS, and suggestions as to whether or not to stick with PZI. If you do that, be sure to put "PZI" in your subject line so you'll hopefully get some PZIers or former PZIers taking a look at his #s. You can also post in the other insulin forums to ask if people think switching is a good idea.