*IF* your Costco has the same cellphone policies that mine did when my family bought a u370, then here are my concerns.
You have fourteen days following the date of purchase to exchange that u370 for a different make and model of phone, and you have 90 days following the date of purchase to exchange the u370 for another u370 if there are any problems with the phone.
And you have, I think, only fourteen days to return the phone for a full refund with no restocking fee charged by Costco.
If you were to exchange that u370 for another u370 in case the dropped cases are affecting just that one particular purchased phone, I don't know if Costco would still permit you to either get a refund or exchange the second u370 for another make/model if it turns out that the second u370 still drops calls.
If you would prefer to do business with Costco instead of another brand of retailer and exchange this u370 for another make/model of phone at Costco, then the LG Octane and LG Cosmos 2 are two other phones with a physical texting keyboard that Costco sells.
The Octane has similar features to the u370 (play music, record videos, take pictures) but the Octane has a lower maximum video recording resolution of 320x240 versus the 640x480 of the u370. Also, when there's a phone call, the ringer is played through speakers that are located on the inside rather than the outside of the phone. So I've read a decent number of complaints that the ringer can be hard to hear when carried deep in a pocket or purse.
One more thing. If you decide to research customer reviews on the internet for the Octane and you're reading the complaints that were filed earlier this year, bear in mind that between January and approximately April the manufacturer LG released several software updates to correct various issues. Supposedly the most severe call quality issues were resolved by verzion 5 of the software released around April or so.
The Cosmos 2 is new enough that there aren't many customer reviews yet by which to gauge its long-term reliability. It plays music but can't record (or play, I think) video. It comes pre-loaded with a program called Daily Scoop that wakes the phone up in the middle of the night with updates; some customers have complained that this waking up night after night is a nuisance and is hastening the draining of the battery between recharges. But supposedly (see below) it can be shut off. And while I was in a Verizon store, I sent a text message to the demonstration Cosmos 2 phone in the store in order to evaluate the phone; the font size that the Cosmos 2 uses to read the text message was surprisingly small. I ran out of time to see if it can be enlarged. Fortunately, the font size for the rest of the Cosmos 2's features is large enough.
Maybe it might be worth calling Verizon's technical support department and seeing if the technician can do any troubleshooting to see if the dropped calls are due not to the u370 but to any problems with Verizon's equipment in your area. And maybe there's a chance that the dropped call problem could be a defect in just that particular purchased phone -- we needed to replace an LG VX8700 flip phone whose inner screen stopped working. Other than that, we've never had any problems with call quality or call strength with that phone; so we bought a new VX8700 from ebay. That second VX8700 had a severe problem where the other person's voice was constantly breaking up.
LG Cosmos 2http://membershipwireless.com/index.cfm/go/shop/do/PhoneDetails/productid/4657
turning off "Daily Scoop"http://community.vzw.com/t5/Wireless-Feature-Questions-Other/LG-Cosmos-Touch-Help-Remove-Daily-Scoop-Please/m-p/618772#M9339