Solved this problem by upgrading drivers for DWA-552. Explanation follows.
I've set up 2 of the 655's. For the first one, I did *not* upgrade the firmware of the router. It came from factory set at A.1 / 1.02. No problems getting clients online which include 2 desktops both using DWA-552, laptop using pre-installed wireless, 2 T-mobile hotspot phones, 2 PSP's, etc. This router has been up and running for about 10 days with no issues.
Then set up the 2nd router (different location, of course) and decided to flash the 655 to 1.05 first. Worked well for less than a day and then connection kept dropping. Router status showed that router could not stay connected to internet for more than an hour before it restarted itself. Exhausted every possibility I could think of and then returned the hardware for a new one.
I still believe first unit was defective. Got better results with the 2nd one, but could not overcome the issue of clients losing connection to router. On this router, clients are 1 desktop with DWA-552, laptop with DWA-652, Hotspot phone, WING cellphone. None of the clients could hold the signal.
Finally, updated the driver on the DWA-552 (desktop adapter). Rebooted the computer. The entire network 'settled down.' Every client gets and keeps the connection. If I turn off the laptop or the WING, they re-establish internet connection as soon as they are turned back on. Router has had steady internet connection for days.
My conclusion is that the driver that ships with the DWA-552 will work with firmware version 1.02 on the DIR-655 router (maybe 1.03 & 1.04 ... didn't try those). If updated to firmware version 1.05, DWA-552 must also have driver updated otherwise it causes 'wi-fi havoc'. Interestingly, I did not have to update the driver for the DWA-652 notebook adapter.