Massive degradation in AT&T service.

I have noticed that in the past two months my AT&T service has gone down the drain.  Let me explain.  At home my LTE signal has always been between -90db-100dbm.  Now I notice it will often fall down to 4G (HSPA).  Even the HSPA signal is horrible.  It will often go to -114dbm on HSPA+.  That told me something is seriously wrong.  I have been using the same phone (iphone 5S).  I even got a new sim card for it, restored it, and set it up as new - problems still persist. My mother's iPhone 5S also demonstrates the exact same problems.  I have not seen a call drop in years until last week.  

So when I called AT&T customer care, the rep advised me to use the Mark the Spot app on my iphone.  I ran the app and it told me AT&T was aware of the problems in my area.  Two days later I got a notification on there telling me the problem has been resolved; however, the data signal is still crap.  LTE pings (latnencies) are still much higher than usual.  Data speeds are generally slower.  

Correct me if I am wrong, but isn't AT&T service suppose to get better and stronger?  I just hope network enhancements are being made to my area so that the service can improve.  It is intolerable to have a good signal for years, then degrade it.

Perhaps T-Mobile wants my business.  Our iPhones are already unlocked.

This is a Chicago suburb.