Like you, I was on 12 Asacol a day and just swiched to Colazal a few days ago too. Given that we were on the same high dosage of Asacol it does seem a bit odd that you're now on a low dosage of 3 Colazal a day and I'm on a high dosage of 12 Colazal a day.
Obviously, apart from other things, the dosage depends on the extent of the disease and whatever other meds you're on. But, do you think it may be that you're not taking enough of the Colazal and that's what is causing the D?
This is just my (uneducated) observation and your GI specialist should know better and be able to offer a more definitive answer Since we've both switched at the same time from the same meds I thought I'd offer an opinion. Hope you're fine soon!