Hmmmm..... Yes, that's much faster than we usually recommend (we generally go up by 0.25U, and not every 48hrs).
6U is a lot of insulin, but some cats do need a lot. It's hard to tell with the pace of increases you have had. It's possible you skipped over the right dose, and the high numbers you are seeing are a result of "bouncing"-- hitting the occasional low number, and then zooming back up in a prolonged reaction (bounces can last up to three days). That said, you tested a fair amount all week last week, and other than maybe the night of the 29th, I don't see many hints that he's coming off his plateau ever.
It's also possible he just needs a lot of insulin. There are several "high dose" conditions that can cause this. We've seen cats on 10, 20, even higher doses of insulin. Again, it's too soon to really say yet if Pumpkin is one of those cats or if he's just doing a lot of bouncing, but something to keep in mind.
What was his starting dose in the very beginning?
Don't give up <3 I also have a ginger cat, they are the best 