Here's a run down of the games Dallas played at OG with the PFF grades to compare to what you or others see.
Buff- RG, 41 snaps. Overall +0.1 Pass +0.4 Run -0.1 0 sacks, 0 hits, 1 hurries
KC - RG, 71 -3.6 -1.5 -2.3 0 sacks, 0 hits, 3 hurries
Oak- RG, 74 -2.5 +1.4 -3.1 0- 0- 0
Jax- LG, 50 snaps. Overall -1.0 Pass -0.9 Run -0.2 - 0- 1- 1
SD - LG, 78 -2.7 -2.3 -1.1 - 0-1- 4
Det- LG, 48 -2.8 -2.6 -0.3 - 0- 0- 3
As you can see, they do not grade him highly in his first year on the field. However, it is not far from being average.
I do not bother to post his grades at RT or a specific pre-season game. Suffice it to say that he was ABSOLUTELY HORRIBLE but, does not matter as he is NOT a RT, and pre-season does not matter.