I agree about the firmware update on your TV, I have a couple Vizio TVs and they pull up and display the display almost immediately, it just takes longer(5 seconds??) for the guide several hours ahead to populate.
I also have a iView tuner and it takes quite a bit longer to populate the guide(15+ seconds) and on the iView if you try and push it, it can even lock up the box for a bit. I'd not recommend the iView for it's guide, unless your kind of patient.
On the iView it's best to tune to the channel for a bit(15 seconds??) before pulling up the guide. Just being tuned to the channel the guide will populate in the background, IOW you don't have to actually have the guide up for it to start downloading guide info.