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Looks like you missed this.

Oops. I saw another post about using another device and assumed the OP did not test this.

To the OP: Do you know anyone with T-Mobile service? If you have an T-Mobile or unlocked LTE capable phone (if your phone uses a micro SIM or a full sized SIM, you will need an adapter), you can put the iPad SIM card into your phone and see if it gets LTE. If you can't test this, you can go to a T-Mobile store and see if any of their phones can get LTE.

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All good suggestions, Hungx. I don't have any other device to confirm LTE, or I would have tried that already. I don't think that T-Mobile is doing maintenance on their towers, because it's been over a month now. I think it's that update pop-up that says something like "Your data provider has a new update". We kept closing it, but it keeps poping up, so we just hit the OK button. It then disappeared. I didn't see any download or update after that, but the problem started then with the slow connections. I'll try pulling out the SIM card. Thanks.

I also had a carrier update and I can get LTE. If a DFU restore doesn't fix the problem, then the problem is with the iPad itself.
 
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