I have a solution, but only for Metro PCS. Go to settings, click more, go to cellular networks. Click access point names. Click the + button on the top right of the screen to add another access point. Change the name to whatever you like. Change APN to fast .metropcs .com (no spaces)
Scroll down to mmsc. Change that to https ://metropcs. mmsmvno .com/mms/wapenc (no spaces) . After that click the three dots on the top right of the screen. Click save, then when you get back to the access point names choose the one you just made. Let your 4g LTE signal refresh then Walla!!!! Downloads from play store are no longer stuck at downloading/ pending