May depend on what Playback setting you have in PPRO.
May depend on your playback CODEC ( can be different in some Project Settings)
May depend on your sequence setting
You don't judge quality using the internal Premiere monitors. They are for seeing content only. Always judge quality, including resolution, on a properly calibrated external TV. If you don't have one hooked up to Premiere, you will have to burn out a Blu-ray and test that way.
I'm viewing the Ppro timeline on a second monitor which runs off of my second graphics card. It's not been professionally calibrated, but I suspect that it's not far off. It's also the monitor that I'm using to view the same file in AE's composition window and Windows Media Player.
Does your comment about not using Premieres' timeline for judging quality still apply?
Yes. You have to use either an AJA or BM card for HD resolution or use a firewire connection for output on an external device for SD resolution.
I'm viewing the Ppro timeline on a second monitor
Don't use a computer monitor. Use a calibrated TV (or professional studio monitor).