4G coverage for Virgin Mobile USA

So I've been with Virgin Mobile USA for a few years now, preferring prepaid monthly service and full priced phones. I recently upgraded to a phone with 4G / LTE capabilities. Virgin is still rolling out 4G coverage in the state of Washington (Bremerton and Tacoma are currently covered, Seattle and Bellevue are currently not). But with that said, there are pockets of areas in Issaquah and Bellevue where my phone registers a 4G / LTE connection. I wonder if this is happening to anyone else. Often times, I'll have coverage when standing at my front door, and will lose it when I move from that spot. Anyway, it's still worth the wait for me since I'm saving so much money. In 2013, I only spent $455 on cell phone service, and the phone I've been using for almost 2 years just sold on eBay for $220. The amount I spend in 2014 is already set to double, since I bought a new phone, but that still PALES in comparison to the $2,300+ I spent on T-Mobile in 2010 for 2 lines (and that does not include the phones I bought that year).