Just freshened up my dash with new gauges and was having trouble with the factory speedometer setup. New speedo gauge was fine, but I'm sure the line was clogged up or pinched somewhere from the pickup on the outdrive.
Not wanting to troubleshoot the old line or pickup too much, I replaced the OEM speedometer setup with this: http://precisionstar.ca
It works great, has a clock, displays LAT/LON coordinates, has a trip odometer, max speed with date and timestamp, made in four different color combos, no GPS puck to mount and has a simple three wire connection. It is a bit pricey, but it just plain works. I purchased the white face gauge with SS trim to match my Teleflex Lido SS gauges.