San Disk Cruzer Glide 3.0 256 GB Slow Copy

I buy a New Cruzer Glide 3.0 256 GB (on Costco) and when I send a file it start to copy fast then slow… but very slow… I Thing is damage because i have one of 64 gb and are very fast when copy (write or read)

Have you taken it back to Coscto and gotten another one? That would be [potentially] the fastest and easiest solution.