Hi there! I've fairly recently, as in this past year, gotten back into the swing of biking -- the result of cleaning out the garage and getting bikes off the ceiling and into a spot they could be accessed

Anyway, I try to ride a bit in the evenings, and usually will do about 2 to 3 hours' riding on the weekend. I'm just shy of six feet tall, and my weight's been teasing me between 200 and 210.

I ride a Diamondback Apex (from about '95) mountain bike, and I didn't have any problems earlier this year. However, I've started developing knee pains (or slightly below the knee pains) while riding, even though I'd raised the seat to a pretty high point (have to dismount to stop); usually the pains develop about an hour to two hours into the ride. I find that while riding, if I change my foot's position to the heel being over the pedal and point my toes down, the pain disappears. However, the pain does persist for about a day afterward, particularly noticeable if I have to do any kind of squatting.

Having taken the bike and myself to a few shops, I've gotten mixed statements from them; most have said the bike itself is too small, while a few have said a couple adjustments could be made to resolve the issue. One of the ones that stated the bike looks small also commented that some adjustments might alleviate my problem. I'm either too used to being on my mountain bike, or am too used to being a sardine, that I don't really notice my current bike as being uncomfortable until a couple hours into it -- which doesn't seem to help me when looking for a comfortable bike to ride.

The type of riding I do is mostly hard-top, asphalt or concrete, though I wouldn't want to risk a road bike with the roads the way they are in this area. Most of the shops recommended a hybrid. However, each pretty much suggests the models they carry: Fuji, Specialized, Cannondale, Raleigh, and since I'm not really an aficionado, I don't really know much about the various makes.

So, after all that the questions I have are fairly straightforward:
How can I tell that a new bike would actually resolve the knee problems?
If I get a hybrid, what bike models are good, solid bikes?
Are there solid US manufacturers still out there?