Defective AMD Radeon HD 7770 ?

I shut off the computer and removed the left panel of the case. The ambient temperature was moderate (I thought that excessive heat might have been an issue). After waiting for about 20 minutes, I turned the computer on again (the case is still open). Half an hour later, the video image seems stable.

Heat can certainly play a factor in a video card's performance. I remember on my old laptop with integrated graphics, if the laptop got too hot, the display would do the same thing as what you described. Once I got a laptop cooler for it, never had that problem.

I would make sure you have a good airflow/ventilation system in your case. If the hot air can't escape, the components start heating up and this can lead to excessive wear and tear and reduced performance.

check temperatures with gpu-z

I've run boxes that are substantially hotter than this cool cat without issue. I once had a "ConoGraphics" prototype unit in my IBM PC (late in 1981) on which I could probably have fried an egg! I suspect that heat is not an issue. I will, however check out GPU-z. Thanks for the reference. =)

Video problems can also be caused by your PSU, if your using the stock PSU, or a bad monitor cable, or the monitor itself. Usually any of these in my experience would cause more static, or colored pixels that follow images around. If yours is shaking I can't be to sure, just something to keep in mind. (I kind wished someone would have told me my monitor could have been bad before telling me to get a new GPU, but I wanted a new GPU soon anyway.)

It sounds like comparing apples to apples, but really it's more like comparing apples to oranges.

I'm not convinced it isn't a matter of heat, but assuming that it isn't, you should try a driver cleaner and reinstall the latest video drivers. If I looked at the right Gateway, your PSU should be sufficient, so ... maybe your refresh rate is set too high?

With respect to heat, I've been running the PC without issue (with one side of the case removed) for about an hour. I'm going to reattach that side and evaluate display performance.

I've not done anything to modify the default refresh rate. I'll have to look into that. Control Panel > Display doesn't seem to offer any refresh rate settings adjustment. Will dig deeper.

Thanks for the helpful input thus far, folks.

is your monitor a ctr or LCD?

LG LCD, 19". Worked without issue on my previous computer. My wife is running the same monitor without issue on her Gateway PC.

Computer case is now totally enclosed: 2:23 PST.