iphone 5s constantly searching for cellular signal

[FrustratedInMN]

In the past 1-2 weeks, I've been having issues with my iPhone 5s.  The phone is constantly searching for a cellular signal and in addition to draining the battery at lightening speed, it's driving me crazy.  I get the 'not delivered' message multiple times when texting...I have to hit the 'try again' button as many as 5 times before the phone catches/hangs on to a signal and completes delivery.  I've been missing calls as well...family and friends asking why I'm not taking their calls but the phone never even rings!

I've removed the case.  I've completed hard and soft reboots.  I've popped out the SIM card.  I've reset the network settings.  I'm completely out of options and extremely frustrated.  iOS is current (8.0.2)

I purchased the 5s in March and had issues with the volume buttons not functioning approximately 2 months ago...Verizon sent me this refurbished phone.  It worked fine for the first few weeks.