I think Jill is spot on with momentum just being lost. It happens. I do think the food switch played a role, as I have seen switches to raw wreak havoc on Sasha's BGs as well as other kitties. It passes once the body adjusts to the raw, but in that time glucose toxicity has built up and you need to power through it with more insulin. He'll come back down in dose once he's spent more time in healing numbers. Just keep increasing the dose as needed until you get back to the all green he once had.
The raw switch, if it took care of the liquipoo and possibly the coughing too, was incredibly beneficial to Mim. Possibly he was allergic to a canned food additive or protein, or even possibly intolerant of particular cooked proteins in general. It is possible for a kitty to be intolerant of a protein in cooked form and do well with it in its raw state. Perhaps he had the beginnings of IBD and the food change worked - it often does for cats with chronic liquipoo.
Allergy testing in cats is notoriously inaccurate, outside of food trials, which you have had success with. IBD doesn't usually show in bloodwork, although IBD and also allergies (which may or may not be linked depending on the animal) can cause elevations in eosinophils and basophils. Those are the white blood cells that respond to allergens and parasites. If Mim had elevations in either of those (eosinophil elevations alone are more common unless the reaction is severe), I would maybe suspect allergies or IBD, but they are not definitive alone for either condition.
Has Mim ever been tested for heartworm? Is he treated with a preventative? I don't know how common it is in Australia, but two symptoms are coughing and vomiting, both of which Mim had. If it were me, I would probably have him tested at some point just to rule it out (which I did with Sasha when she had the same symptoms). There is a possibility always of Toxoplasmosis infection with a raw diet (or anything that he may have ever ingested that was infected with it), and that can elevate BGs as well as cause vomiting, coughing, and liquipoo. That may be a test to run also just in case, although may cats are infected with it and are asymptomatic.
More On Toxoplasmosis:
http://www.vet.cornell.edu/fhc/brochures/toxo.html
http://www.peteducation.com/article.cfm ... 34&aid=770
http://www.fabcats.org/cat_group/policy ... /toxo.html
More On Heartworm:
http://www.sniksnak.com/cathealth/heartworms.html
http://www.cat-world.com.au/heartworm-in-cats
http://www.peteducation.com/article.cfm ... 42&aid=742