M.C.
How funny we all say the same thing.
My daughter had the same problem switching to whole milk.
It took a little over a week to make the switch
Day 1
12 oz bottle-I would make a 12 oz bottle and pour out 1 oz and then pour in milk.
Day 2
I would try same thing but add 10oz formula and 2oz whole milk.
That is if the day before went well.
If she doesnt immediatly notice-make the next change on the next bottle.
If she would fight it I would move back to the previous bottle that she accepted.
I did this until she was fully did the switch. Some days she would stay at the same level for 2-3 days until she was use to it.
I also did this to later, to switch her from whole milk to 2% or lowfat milk.
Good Luck