Default M8 GPE Doesn't Switch to 3G?

My M8 GPE doesn't automatically switch between LTE and 3G depending on signal strength like my iPhone does (and as they always have). That leaves me with my phone always sitting with 0 to 2 bars at home and at school, and it hurts battery life. I get solid LTE while I'm outside, but horrible LTE while I'm inside at school and at home. If I manually switch to 3G, I get full bars of service indoors, but it's really annoying to do that all the time. Is Android supposed to switch network types on the fly? If not, is there an so that will do it for me? Thanks!

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