Belkin Router Firmware problems

Hello all, it's been a good while since I've been on here, but lets get down to business. I currently own a Belkin N300 Wireless N Router with the Model beingF9k1002V5. It's rather cheap, $35 dollars, only uses 2.4ghz, and really simple but it has handled all my needs for WiFi with class and style (topped out at around 60 devices on at once with full speed WiFi. Impressive if I do say so myself.)

The problem is that with the current firmware I had on the router (Firmware F9k1002_WW_5.00.15.bin) My windows 8 tablet can't connect to the internet. It always got a "Limited" connection. To solve this problem I downgraded the firmware to 5.00.08, and the tablet was able to get a full connection.

While on 5.00.08, the router would go offline and you would have to constantly restart it, and this became an issue, so I downloaded another firmware off the internet, 4.00.06, thinking this would solve the problem. I installed it, and the problem was fixed, but now the WiFi range for my router really sucks, and the connection speed is horrible. I went to reinstall 5.00.15, but now I get an error that says "Update file is not the correct type or version for this device. Upgrade failed. Please obtain the correct file and try again.

Some things that I noticed is that the whole UI for the router control panel changed. Also in the control panel it says that I have an F9K1002V4 when I have a F9k1002V5. How do I fix this?

I heard about a tomato firmware. If this is good, how do I install that?