Here is my issue

I have an HTC Raider/Vivid (Bell Device) and its unlocked and I am using a Telus sim in the device. Just recently I have only been able to download random apps from the market over 3G while others wont work at all. I can download anything over wifi? \

I had the same issue with the Nexus recently and when i did a hard reset on the device it was fine after that.

Any suggestions on how to fix this?