I am sorry for your trouble.
I have a K-7 since late November and I do a fair amount of Hi continuous shooting, with sequences of 15 to 100 shots each time.
I use typicaly 6Mp JPEG (only) with a Sandisk Extreme III, and I can easily do 10 to 20 s in Hi continuous shooting mode. I just need to remember to kill off all PP everytime. In 2 Mp JPEG, I can do easly 30 s or more in Hi continuous shooting.
First a few points for all Pentaxians: in Hi continuous shooting, you need to disconnect/switch off all in-camera PP incl. lens distortion correction. Beware that the default settings (eg with the K-7) do include some PP.
You must also have a good/fast SD card like a Sandisk Extreme III. You also need to be in MF or AF-S. (Do not use AF-C.)
With RAW or RAW+, you should be able to shoot at least 3 s in Hi continuous shooting, before the buffer is full and the camera slow down.
From your description, you did some thorough testing, and your camera need to send back to Pentax.
Hope that the comments will assist...