It is probably in MLS archives, but Frito-Lay came on at the same time as Gatorade IIRC. Not surprising as they are under PepsiCo. Perhaps Pepsi will switch out some logos of other shirts. (I think they have 3). http://www.mlsnet.com/content/02/mls1030pepsi.html
Frito Lay became a sponsor in 2002 with the "Chips are Salty" deal. Since then the MLS has encountered many .....STOP CRAPPING IN MY HAT!