When I import avchd files from my sdhc card its very slow. 1.4 minutes of video takes nearly 5 minutes to import its the mixdown that takes the time. My computer is new and a good specification.
Maybe because you have way to many things going on at the same time. Tell us what is your specs for your "new" computer.
There is a limit. Inorder to import avchd files, you need either 3.3Ghz and up or Quad-core at 2.8Ghz and up or something like that.
Chack the help for importing AVCHD.