I have the same issue. About a month ago, I got FULL 4G HSPA+ Coverage then since then I am getting 1-2 bars. I don't know whats up. I've called T-Mobile about this issue and they can't give me an exact answer. 80007 is my zip. Closest intersection to me is 64th & McIntyre st Arvada Colorado.
My cell tower info:
52561 cell id short
21155153 Cell id long
11096 LAC ( local area code)