>Again, I say try it.  This 'cleaned up' version works on my MPLAB:
>
>
>ADD     MOVF    AL,W    ;low byte
>        ADDWF   BL,F
>
>        MOVF    AML,W   ;Middle low byte
>        SKPNC
>         INCFSZ AML,W
>          ADDWF BML,F
>
>        MOVF    AMH,W   ;Middle high byte
>        SKPNC
>         INCFSZ AMH,W

you are right, i confused the incfsz with an incf.
how does BMH ever get added to AMH if the next instruction is skipped?


>          ADDWF BMH,F
>
>        MOVF    AH,W    ;High byte
>        SKPNC
>         INCFSZ AH,W
>          ADDWF BH,F
>