Throw in an updated Tow launcher, should help on that.
Since the Abrams is ALREADY capable of defeating anyone else's tanks 1-on-1 (and even 1 on 3 or 4), why add another AT weapon? The 120 mm gun is good enough.
Again, the addition of a TOW launcher would entail major design changes, added weight, increased profile, not to mention that when you add something, something else has to go.
The M1 is good to go, as is. The only improvements that should be made should concern themselves with mobility and protection (other than cupolas and gun shields). Not firepower.