jpf, Check the search function. I believe within the last month or so there was a post similar to yours and the remedy was cleaning the water valve at the toilet.
Rick.
I just found the post, The thread is named "Sluggish Toilet" in the maintenance section of the forum.
2005 Montana 3670
2005 Chevy 2500HD D/A
Pullrite SuperGlide
Prodigy/Intella-Stop
Doran Pressure Pro
Ride Rite air bags
In-cab controller