Although it doesn't make much sense scientifically, some patients don't tolerate certain formulation as well as others. Sometimes, it is not so much the actual drug but the makeup of the pill (other components such as binders, etc) that some patients may not tolerate well. As far as splitting the pill, it is not a problem with metopolol. But there are some pills that shouldn't be split. Consider going back to the original torpol XL.
you won't be on a time release with standard metoprolol that is why you need to take it twice a day. I don't know why you have to cut in in half, Wal-Mart has generic metoprolol in 25mg tablets for $4.00 per 30
The problem with cutting a pill in half is that while the whole tablet contains 50mg of medicine, you don't know if it is evenly dispersed thorught out the whole tablet (it should be though)
Many people report these types of things when switching from a brand name to a generic. Just look up coumadin vs warfarin.
Did you doctor change your script for insurance reasons?