VZW HTC 10 on AT&T now, need help

[AKFL3TCH3R]

I'd like some help with getting 4G LTE from my new carrier! Anyone know what to do? Never done this kinda thing before. Some APN stuff?

 

[B. Diddy]

Go to Settings>Mobile Networks>Preferred Network Type, and make sure it includes LTE.

Part of the problem might be that the LTE bands that your HTC 10 supports don't include AT&T's main LTE band, which is 17:

verizonwireless.com/smartphones/htc-10/
Cheat sheet: which 4G LTE bands do AT&T, Verizon, T-Mobile and Sprint use in the USA?

So if AT&T's other LTE bands (2, 4, 5) aren't particularly strong in your area, that might lead to overall poor or absent LTE reception on your phone.