Test this, boot with a live Gentoo the same kernel. If this works, copy the running Kernelconfiguration to your system. Yes there are a lot of things there, but only for testing it should work.

Code:

add some chroot....
zcat /proc/config.gz > /usr/src/linux/.config
make -j? && make modules_install

Do this not work, add all available SATAdriver to your kernel, but not as modul. Maybe this is the problem. On my installations satadriver are the most problems.

For information: When you use an SSD, use the noop sheduler for HDDs, and set the "discard" Option in fstab for ssd.

Greetings
darktux