This tree has had enough damage that you will probably want to start with a new tree. I doubt that this was entirely winter kill, but that may have helped. You mentioned cutting suckers from the base of the tree, and if the tree has growth in the crown (which it does), that usually means that there is damage at the ground level. This could be mechanical damage, like grass cutting equipment getting too close, and cutting/scraping through the bark. Or, it may be bacterial canker, or similar. Without pictures of the damage, I won't be quite sure what it is.
You also mentioned ants coming out of the tree. Unless there is a food source for the ants inside the tree (unlikely), This signifies at least the start of a nest. That means the inside of the tree is being hollowed out. Look for 'sawdust' around the ants' entry point if you want to be sure.
The damage to the tree could have been prevented (as always), but it was most likely caused by (neglect from) the previous homeowner. Because these cases do not generally turn out well, I'd recommend starting with a new tree. Get a tree that is disease resistant in your area, and keep close track of any abnormal developments. If you are careful around the tree, and keep it fertilized and watered, you will be rewarded with a healthy tree that resists pest and diseases on it's own.
If you do notice the start of what looks like disease, you can have it looked at right away, ideally by a certified plant health care professional. Most disease and pest problems are easy to take care of, if the tree is healthy and growing well.
If you are not interested in starting anew, you will have to verify what the damage is, so you can prescribe proper treatment. A healthy tree has an unbroken layer of live cambium under the bark over the entire trunk and branch structure. Look for cracks, cuts, holes, dead patches, canker, etc. where disease might enter. Again, this tree (if it can recover) will never be very healthy or attractive, and it would be highly recommended that you start with a new tree.