Are the Vikings depending on Brett Favre too much?

In the Steelers game, they had 1st and goal at the 1. After 1 run they tried to p. Why didn't they give it to AP 2 more times up the middle? Also Brett Favre threw the ball 51 times that game. You can see that he can't sustain his accuracy the more he throws. I'm not sure if he can make it the whole season. Anyone else see him fading late in the season?