Copied from another post here...I was looking also. =)

GUTHRIE'S SAUCE
Board: Copycat/Restaurant Recipe Requests at Recipelink.com
From: Auburn Masters '95 1-25-1999

I fiddled with the recipe, and here is what I found was the closest.

1/2 cup mayonnaise (I used Kraft)
1/4 cup Heniz Ketchup
1/2 teaspoon garlic powder
1/4 teaspoon Worcestershire sauce
ground black pepper

Mix together the mayonnaise, ketchup, and garlic powder. Add the Worcestershire. Stir. Then sprinkle enough black pepper to cover the mixture. Stir. Then add ANOTHER layer of black pepper. Stir again.

This comes the closest of any combination I tried.