Popping at altitude was a well known problem when I worked in a potato chip company years ago. The amount of air in each bag for optimum product protection and for presentation is quite high and the expansion at altitude is greater than most people imagine. To be honest I don't think changing the packaging materials or sealer setting is going to help, although you could of course try it out. The suggestion about an expansion seal made by SQFConsultant is pretty innovative but might not be possible in a traditional flow wrapper machine. Also, after the expansion section had 'popped' at altitude and the packages were back at sea level on the west coast you would end up with a very floppy unattractive package that looks underfilled.
When I worked in snackfood we used to make special production runs of chips specifically to be used by airline caterers and to be shipped to towns in the Australian Alps. These product runs were packed with much less air then normal runs. They didn't pop at altitude but looked floppy and awful at sea level so I don't think that doing the same thing for your west coast orders will be the ideal solution - no doubt this is why you posted your question.
Three options to consider:
1. Pack product for the west cost inside a sealed poly inner inside the cardboard shipper cartons. This will keep the air pressure around the outside of the chip packets constant and prevent popping. You will need to minimise the air in the poly liner bag or the liner will pop.
2. Find a transport method or route that does not pass through high altitude locations.
3. Engage a copacker or contract manufacturer on the west coast.
Good luck with it!