A couple days ago, after much research I picked up the 25" Acer H257HU IPS monitor (60 Hz, 4ms). I went from a 24" 1200p TN panel to this. At 25", the dot pitch is tiny lol.

http://us.acer.com/ac/en/...ent/model/UM.KH7AA.001

Sometimes, I notice the frame rate becomes sluggish/choppy even though the FPS are quite decent. In Fallout 4, this happens periodically. With Dirt 3, no issues (completely smooth).

I'm using an i7 920 at stock and GTX 670 4GB on the DisplayPort.

Any ideas?

Was it like that with your old monitor?

No, it wasn't.  Previously, I was using DVI, now I'm using DP (1.2).  It is almost as if it feels like 10 FPS when it's actually 40 FPS, and the mouse pointer lags when you move it.  I've tried it with and without AA.
 
Even when logging into Steam, the friends who are already logged in stutter in movement when they pop up on the right.
 
 

I spoke to Acer and they said I should take it back.
 
It's too bad, because the colours are amazing.

What you are experiencing was what I had but with an older card and driver. My setup at that time was a 27 inch Overlord Tempest and an EVGA 770 classified. Prior to the release of Fallout 4 I had absolutely no problems running anything that I had at a smooth 60 FPS. (even Skyrim) V-Sync was enabled and I was running an aged driver. My thinking was that my 770 would handle FO 4 maxed out and that is where I set it. I did have to manually type in the 2560 1440 setting for my monitor as it did not do it automatically. That should have been my first clue based on past setups. 
 
It didn't take very long at max settings for me to realize that my 770 was being pushed around and if I wanted to play at this resolution and maxed out I needed some extra horse power. My current video setup now is the same monitor/resolution and a lot newer driver 358.91 with a butt kicking EVGA 980 TI SC. Problems solved and it's game on.
 
I was and still am running a Z87 ASUS Hero board with a 4770 K chip at stock speed.
 
 

So, my GPU isn't up to the standard for 1440p? As I said earlier though, when I just join Steam and my online friends pop up, its animation isn't smooth. In Precison X, I get 40-50 FPS in games yet sometimes feels like a slideshow.

NazcaC2
So, my GPU isn't up to the standard for 1440p? As I said earlier though, when I just join Steam and my online friends pop up, its animation isn't smooth. In Precison X, I get 40-50 FPS in games yet sometimes feels like a slideshow.

That's what it sounds like to me. You didn't mention what driver version you are on.
 
If Acer recommended that you return the monitor I would do as suggested.

You're running an older GPU and CPU on a 2K monitor I assume. Before you decide to return the monitor try some overclocking on the CPU and GPU (if your PSU is capable enough) and see if there is improvement.

Currently, my NVIDIA driver is:  359.06
 
GPU:  GTX 670 4GB
CPU:  i7 920 on the X58 chipset
 
It's just weird that when I'm not even playing any games and my online friends appear, they pop up from the right in like a jumpy 3-frame animation.  And, when the FPS says it's quite decent, it appears not as smooth.  I'm just confused.

Update:  I performed a clean installation of the newest driver and it seems to have fixed the choppy animation problem with the Steam friends popping up.  Now to test other things...
 
Strange.  I didn't think I would need to reinstall the GPU driver because of a new monitor.