New external drive for Time Machine won't complete a backup using Airport Extreme

I recently upgraded to a larger external drive (Seagate's Backup Plus for Mac 8T (STEM8000400) for my Airport Extreme Base Station (MC414LL/A) . It's been a few weeks now and there hasn't been one successful backup completed via Airport and the little that it does back-up is painfully slow.

• Time Machine will back-up for several minutes, then just stop.
• I've tried turning off Energy Saver overnight, still no luck
• Seagate drive is formatted to Mac Journaled
• I've trashed the existing back-up file, reformatted the drive, etc.
• My previous drive, a G-drive, worked perfectly with Airport Extreme
• To test the drive, I connected the Seagate drive directly to the computer (vs. Airport Extreme) and was able to get a full back-up, but I don't want the drive on my desk.

Thanks in advance for any insight.