The speedometer was the larger headache. The '04 and '05 tracs use SCP multiplexing to send the tach, speed and I think temperature outputs to the hybrid cluster. I tried, swapping the abs modules, wiring in the G-force sensor and wiring the speed output from the abs to the PCM hoping the PCM and cluster would communicate the speed and tach info through the SCP, but that did not work. With that config, I had no speed, no tach and no odometer, but the engine temp worked which I thought was strange. The PCM was also receiving the speed and tach, as it read correctly on the scan tool through the OBD II, but nothing on the cluster. This setup also threw abs codes which I couldn't get rid of. My theory is that the speed and tach signals go through some further conditioning at the PCM so as to be output on the cluster or that the cluster and PCM have to match in order to it to work as a way to safeguard against odometer tampering, but that's only a guess. Another possibility which I did not try was to dig into the cluster programming to see if it could be reset or reprogrammed to make it work.
My solution was to keep the '05 abs unit as is, use a Dakota Digital SGI-5E for the speed signal conversion, swap out the clusters and wire in the '99 GEM module (I actually used a '03 trac cluster i got off ebay as I liked the look better). This was a pain and I lost auto headlights along with a couple other bugs I'm still trying to work out, but I got the tach and speed working, which was worth it. The Dakota Digital gets it's input from the + VSS signal coming into the ABS and the output gets spliced into the VSS signal going to the PCM and other components. The hardest part was wiring the GEM as the hybrid '05 cluster does a lot of what the GEM does on the '99-'01 explorers and the wiring is very different. I have all the pin outs mapped in excel that I will clean up and post at some point.
As of now, I don't have auto headlights, the seat belt indicator works only for the first few minutes and there is no warning chime, I have an airbag code for a indicator circuit short to ground and no cruise. I think a lot of these would be fixed if I used a '02-'03 trac GEM instead of the '99 GEM as the wiring for these functions are far more similar between the '02-'03 and '05 tracs as opposed to the '99 explorer and the '05 trac. The wiring diagrams for each truck will be your best friend.