First, I don't think DAC0L is in external RAM. You shouldn't be using MOVX there.

Second, your program doesn't have an end. Sure it says END, but that's only to inform your assembler that that's the end of your file. So end your program with a dead end loop (sjmp $), or even better, set the IDLE bit in the PCON register to stop the CPU (saves power!).

Third, the ADC and DAC are 12-bit, you are only using the lower 8 bits. Spooky. If you want to use 8 bits, you should be using the highest 8 bits.