Group Text - Delayed Texts and repeated Message Send Failures

Iphone 6 running iOS 8.3. On group messaging (iphones and android/windows phones), I constantly get delayed texts coming in (sometimes hours or even a day later). And every time I turn off/turn on my phone, I get message received failures for texted pictures that never come/came through (some pictures come through while others never do).

The entire group has deleted and re-started the group message several times in an effort to fix what is my issue alone. This happened as well on my 5S (and has carried over to my new 6 purchased just a few wks ago). No doubt this is an ATT/carrier issue and not the phone....

I have a microcell but the same things happens when away from the microcell and/or wifi (but it does seem worse when connected to wifi and microcell).  Settings  - Imessage ON, SMS ON, MMS messaging ON, group messaging ON.