GT,
[Walker] is one of the fastest guys on the field
I'm not sure where you got this, but Walker is not that fast. He ran a 4.49. That is very average for a wide receiver, which is exactly why they moved him to TE. He's pretty fast for a TE, except on our team he's a truck compared to Vernon. Then again, pretty much everyone on the team is a truck compared to Vernon.

40 teams for our skill position players:
Ginn: 4.35
Vernon: 4.38
Jenkins: 4.39
Kyle Williams: 4.43
Crabtree: 4.48
Walker: 4.49
Celek: 4.65

*Moss: 4.25 (at the Combine); 4.4 now

James: 4.45
Hunter: 4.46
Dixon: 4.54
Gore: 4.65

Kaep: 4.43 (what he says he ran once)
Alex: 4.71

In other words, Walker is the 10th fastest of our skills position players. When he is on the field, he is probably the 4th or 5th fastest guy, depending on who the running back is. 4.49 is solid, and it matches up really well against linebackers, but he isn't on the field because of his overall speed.