I wonder which 3 or 4 groove pitarm on my cousin 2003 1500hd gmc serria. Let me know.

 

Either take the old one off and head to the parts store or get both and take the one back you don't need. There is really no other way of knowing. If you get the nut off you might be able to tell but at that point you already have the truck tore apart so you might as well have both on hand. Even if you go to the dealer with VIN number in hand they won't be able to tell you which one you need.

 

Will look at no problem.