I've got a DW4 on my '98 and a DW5 on the '04. The '04 warms up much quicker. Go for the DW5. I bought the DW5 from Gregg Landry at Lubrication Specialists. That was the best price I could find, and about 200 less that what I paid for the DW4 in '98. Real good guy to deal with and he will walk you through the install. He also helped me resolve a problem I had with my DW4.
Kim
Kim