I've read quite a few comments on signal deteriorating in many areas. I've experienced the exact same issue and today, right now in fact, is the worst it's been. I get 2 Mbps download, which is the worst I've had in the 10+ years being a Verizon customer. I've never seen speeds that low... Ever!
I live in 71423 area code and I've had good signal until just recently, even our LTE internet service is effected to the point we can't watch a movie or YouTube or just about anything with 2Mbps speed. Come to think about it, I too switched my plan as well, just as another person commented on, but that shouldn't have effected my internet plan.
I would like to think the mobile carriers have to be making good enough money to maintain quality service to everyone, regardless of their plan.