My Cherokee Six now has dual G5's and I love the GPSS steering of my original Piper AutoControl III autopilot. Works like a champ!
True, I don't have altitude hold, but it's really nice having George hold the course on long flights. I also routinely have George assist with IFR approaches.
The caveat for me is the AutoControl III required that I retain my old AI, which I moved to a different location on my panel. Which means I had to keep the vacuum pump.
No big deal. I basically have a 5 different places to go for attitude reference while flying hard IFR: The 2 G5's each with battery backup, the original vacuum AI, the Avidiyne IFD 550's synthetic vision, and the ForeFlight/Stratus 2S with synth vision.
Once the TruTrak is fully tested with G5's, I'll look into replace the old George (45 years old) with the new Young Turk!
For now, I'm REALLY happy with how things are working and I'll take the risk of having to replace the vacuum pump.