Why is my Apple Wi-Fi so dead?

Hello Reader:

I have an iMAC 21.5", Late 2013 running OS X Yosemite 10.10.4. I have an iPhone 6+, iPad Air (only wi-fi) & a MacBook Air 13", Mid 2013 Running the same OS X.

I cannot say if this problem occurs on my laptop. It is not used regularly. But I definitely can tell that my iPhone & iPad are.

My Wi-fi keeps taking way too long, INTERMITTENTLY. It does not matter if I'm looking at the iTunes Store or if I'm downloading a page in Safari or other things requiring Wi-Fi.

My download speeds on the iMAC are fine 21.x & 22.x. I have U-Verse through at&t. The problem does occur whether I use my U-Verse Box Wi-fi or my refurbished T Wi-fi Time Capsule Version 7.6.4. Connection is DHCP. Router Mode: Off(Bridge Mode).

I hope this information is helpful to whomever is reading this. Thank you for any thoughts you may have.