Sick iMac - Help needed!

Question

_My set-up:_
24" iMac 2.8GHz, 4GB RAM, 320GB hard drive
15.4" MacBook Pro, 2.4GHz, 4GB RAM, 200GB hard drive
Airport Extreme 802.11n
AppleCare
_The problems:_
1) My iMac will routinely, more often than not, have extremely slow connection speeds to the internet. I get sub-dial up speeds. Pages will often hang for extended periods before loading (even simple pages like Google) or will simply not load at all. When I can get the speed test page to load, it shows an extremely slow rate of speed. I have no other applications running at the same time. I test it out with the MacBook Pro and it blazes along as it should. (I recognize I need to take the speed tests with a large grain of salt. The number displayed on the test site simply validates what I am already experiencing. the other proof is in the glaring difference between the iMac and the MBP.)
I cannot understand this poor connection issue. The APE is about 12 inches from both the iMac and the MBP.
Not only has the problem returned but it is more consistent than ever.
2) The iMac seems to have slowed down some. For example, when I click on my profile name it often takes 3 or 4 seconds for the text entry box to come up so that I can enter my password.
I have almost no data on there. I keep everything on an external drive. I have only a few other programs installed. I did a clean install of Leopard but the problem persists.
Normally, I wouldn't be overly concerned about a few seconds, but it wasn't like this when I first got it. This problem has arisen and I don't want it to progress to unacceptable levels. Therefore, I want to nip it in the bud now.
_The Beginning of a Solution??:_
I took the iMac and the APE to my authorized service tech today (Simply Computing). Their tech tested the machine and verified that it is getting horrible connectivity in Leopard. He booted the machine from an external drive running Tiger and said it worked perfectly, as it should.
He said that he had done some looking on the internet and found slow wireless connections to be a common problem with new iMacs with Leopard.
He didn't say anything about the general slowness issue.
He suggested I call Apple and inquire about possible avenues to resolve the problem. The tech thought that Apple would first suggest replacing the WiFi card in the iMac, although he said that was pointless as it works perfectly with Tiger rather than Leopard.
I called Apple. I was on the phone for an hour and 1 0 minutes. All to no avail. The first person I spoke with told me it was impossible for the tech to run Tiger on my machine as you could not go backwards in OS's. The second guy tried to blame the third party RAM (as the machine shipped with 1GB and now has 4GB on it). I tried to explain that the tech said it passed hardware tests. At the end, Apple said they would call the tech.
I called the tech back shortly thereafter. He had gone home for the day and, if Apple did call (although the store said they hadn't), he wasn't there to take it. The guy I spoke with at the shop expressed some frustration with the Apple Support line. Anyways, he said if it is Leopard then it is a software issue and I'm on the hook for it. I asked how can I be responsible for a clean install not responding to the hardware. He said they would try to isolate it further, ie, switch hard drives and see if Leopard works. He suggested perhaps it is a bad sector or something on the drive. He said that sometimes disks scan and test as if they are fine but continue to not work. This problem can be isolated by switching the drive. If the new one works it must have been the old drive.
Ultimately, he said they were going to do what they could to take care of me. (It's worth noting that Simply Computing in Langley, BC, is an awesome shop to deal with. Always very helpful, informative and friendly.)
I am told to wait until the tech is in on Monday. He'll do some more checking, get in touch with Apple and see what's what. He also suggested I speak with someone at Apple higher up than Tech Support or Product Specialist.
_More Info:_
I called a guy I know who is very experienced with Macs. He said the wireless thing is just a quirk with Leopard being a new OS and that I should just tough it out until a software/firmware release fixes the issue. He also said that some lag time is normal for Leopard to bring up the password entry box on log-in.
_My Questions:_
1) Has anyone heard of these types of technical problems? Any solutions or suggestions?
2) Any suggestions for dealing with Apple to have this successfully resolved. I want my computer to work as it should.
3) Are these problems actually problems or am I making mountains out of molehills? Is this stuff to be expected with the machine/OS or am I experiencing abnormal issues?
I am sorry this is so long winded... I am at the end of my rope. It is funny, this is my first Mac. I switched about a month ago from a PC because I was tired of all the issues that arose with it. I came to Mac to avoid some of these issues. I didn't come with unrealistic expectations that I would never have computer problems again. I just didn't expect to be told to suck it up; that it is part of the OS and it won't work right until future versions.
Any and all advice would be greatly appreciated. Thanks in advance.
Mac&Cheesey

Answer 1

Since the Airport Extreme is so close to the iMac, does the problem go away if you use an Ethernet cable (best if it's cat 5e or better) instead of wireless?
Another thing you can try is to open System Preferences to the Network pane.
All of your possible network services are listed in the left sidebar. Whatever service you are using, Airport or Built-in Ethernet, move it to the top of the list. You do this by clicking on the little gear icon below the list and selecting +Set Service Order+. You may want to restart.
You can also try removing services you do not use for networking, such as Bluetooth and FireWire (highlight service and click the minus sign). This only disables them for networking. Bluetooth and FireWire will still work for connecting devices. You can add them back later by clicking the plus sign.