Hi,
I found the information in the datasheet of 16F628A (page 97) on two options for internal clock, 4 MHz and 37 KHz. I got to work with 37 KHZ doing PCON.3 register = 0.
Then it's got to be a typo in the datasheet, either yours or mine because it does say 48kHz where I look:

A software programmable dual-speed oscillator mode
is provided when the PIC16F627A/628A/648A is
configured in the INTOSC oscillator mode. This feature
allows users to dynamically toggle the oscillator speed
between 4 MHz and 48 kHz nominal in the INTOSC
mode.
Make sure you always download your datasheets directly from Microchip as they will always have the latest versions.

/Henrik.