What name brand laundry detergent is best for removing grease and skank?

My son works at a fast food place and has tan t-shirts that are just grease spotted and greasy smell saturated. I was using Dawn dishwashing liquid and hot water, but the shirts are now just so greasy that isn't working anymore. I never buy name brand pricey detergents, but would if it would get these Ts actually clean. I usually use Purex or a store brand. Anyone sold on Era or Whisk?, or have other grease removing suggestions?