I have ordered Palomino Granbury and the gray streak through the stone is slightly wider than the samples that I looked at. Is this normal?

Yes, the gray streak is formed by minerals in the stone over thousands of years. The gray streak varies considerably from stone to stone, in fact some Palomino Granbury pieces have very little or no gray streak. You can be certain that in a particular load that a large percentage of the stones will have a definite gray streak. Many will have a wide streak, while others the line is very thin.