Why is the network signal strength on my Z3 so much weaker then my old V?

Okay. I have had my new Z3 for a while now and I love everything about the phone, accept for the reception quality. I am on AT&T and I travel in the same area routinly and I always had great reception in my normal travel area with my old Xperia V. At my home I always had 4 to 5 bars of signal. My new Z3 never gets more then 1 bar, if any. I almost never had dropped calls on my V no matter where I went. My Z3 drops calls all the time. My mom lives 150 miles away and I go to visit her at least twice a month. Many times I have driven the entire way while talking on my phone (with my BT headset) and never had a dropped call. I have been to her house several times since I got this Z3 and I have no signal about 80% of the time. I could not make a call if my life depended on it. At first I thought that the problem was that my V was using 3G towers and my new Z3 is using 4G towers. But I swtiched my Z3 to 3G only and it still has not signal in areas where my V used to have 4 to 5 bars.

As far as specs go, the Z3 (D6603) has all the same bands that the V has and more. The Z3 works on all the following 3G and 4G bands.

3G Network HSDPA 850 / 900 / 1700 / 1900 / 2100
4G Network LTE band 1(2100), 2(1900), 3(1800), 4(1700/2100), 5(850), 7(2600), 8(900), 13(700), 17(700), 20(800)


These are the bands the Xperia V operates on:

3G bands HSDPA 850 / 900 / 2100

4G bands LTE band 1(2100), 3(1800), 5(850), 7(2600), 20(800)


So what is the problem here? Why is the reception so bad on the Z3?

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