I've hesitated posting this, but since you're still having problems I probably should share that in my experience one can't always rely on a monitor's self-test to always come up with accurate info. Case in point: I still have an old monitor whose self-test tells me it's fine, yet the RGB (Red, Green, Blue) circuit for red died long ago. Mostly everything on screen displays in yellows and greens - rendering the display virtually unreadable - and it's clearly NOT fine despite what the self-test says (I only keep it around as a backup should something happen to my main monitor and I need something to use while I either have the main one fixed or I look for a new one). Self-tests are NOT infallible. And although I have no way of knowing how honestly the Gateway techs you've talked to operate, I do know that many companies aren't about to admit that. They'll say things like you "could" send the monitor in for replacement, never that you "should," and they will especially never use the phrase "I would recommend that you send it back" because their bottom line isn't necessarily to make sure their customers' systems are working properly - it's to save their company as much expense and hassle as possible.
Food for thought...
Further update - I installed the drivers that came with the card. It offered a lot of options for adjusting all sorts of settings. For resolution I found that 848 x 480 (which wasn't available under plain Windows) fixed the problem. However, I had to use buttons on the monitor to adjust vertical and horizontal to get things right.
So, that problem is solved, but now a lot of the fonts are too big. I can't see as much of a document at once, some other things appear a bit distorted. The pictures here for the daily "scenes" are too long. I can't see the whole picture and the caption at the same time, as I did before.
A resolution of 848X480 is non-standard and shouldn't actually fill the monitor screen. Standard resolutions use a 4:3 ratio: 640X480, 800X600, 1024X768, 1280X960, 1400X1050, 1600X1200, etc. Another example of a non-standard resolution is that my monitor has an option for 1280X1024, which is a 5:4 ratio, and which doesn't fill the screen - there are approximately 86 extra black pixels on both the right and left sides of the display - and if I was to adjust the display with my monoitor's horizontal controls so that it would fill the screen, I'd be distorting the way it's supposed to display. 848X480 is an extremely non-standard ratio of 5.3:3, and it's designed to display with 78 extra black pixels on both the top and bottom of the screen. Adjusting the display with a monoitor's vertical controls so that it would fill the screen would really distort the way it's designed to appear.
Latest update - it's back to the way it was. Apparently the video card didn't help at all!!
The latest from Gateway is that there is a problem on the motherboard. ... (By the way, she said it was the AGP slot on the motherboard. However, I pointed out that the original video card is integrated on the motherboard. That AGP slot wasn't used until I got the new card. She still thinks it's the motherboard. I don't know whether to believe it or not.)
Anyone have any suggestions?
Sad to say, but it sounds to me like these people really have no idea what the problem actually is and they're simply pulling reasons out of a hat at this point. You rightly point out that the AGP slot would have had absolutely nothing to do with your original problem - though that still doesn't positively rule out a problem with the motherboard. However, to me the only constant in all this is that you're still using the same monitor. Is there really no way that you can see if the monitor works fine on another computer? Until you're absolutely positive that the monitor itself isn't malfunctioning in some way, I wouldn't suggest accepting any more hardware from them or causing yourself any more expense.