To use the GPS for ground speed, you will have to have radar simulation.  I don't know if the GPS 1000 has radar simulation capabilities or not.  The PF 3000 will need NEMA output.  NEMA and radar simulation are 2 different things.  You can not have both from the same cable at the same time.  You will have to have 2 cables from the GPS for that to work.  Your other option would be to use something like the Loup sky speed convertor.  The Loup takes NEMA and converts it to radar pulses.  You could then use a splitter cable to feed the Loup and the PF 3000.  Again, I don't know if the GPS 1000 does radar simulation on it own or not.