Problem gone (for now anyway). Get this, On the Hardware Acceleration Tab the first option had been Greyed Out since initially installed and was in regard to enabling Acceleration Cuda & I believe Radeon cards. I assumed this meant it was "force activated by the software I guess. I did check the box underneath "Enable Hardware Encoding".
After your post about Cust. Improv. Prog., etc. I unchecked enable Hardware Acceleration & CIP & did a test Project Save to no avail. Restarted PD13 went back to Preferences and now under Hardware Acceleration Tab the first option is now available to me and now reads "Enable OpenCL technology to speed up video effect preview rendering". Also an Open CL logo appears next to the True Velocity 4 logo at the bottom of the requester. I checked both options and it looks like all is well once again. Go figure!
Thank you very much for your assistance.
I hope you can find a quick solution to the Dual-Preview issue.