My pyrometer is rather erratic too. I talked to Autometer about this and they said that due to the length of wire from the probe to the gauge that interference is very possible.
More boost oddities - 15 psi when we left home then I noticed a max of about 11.5 psi after about 75 miles. Economy was good - 28.6 mpg on this most recent tank.
Viewed from underneath (I will add a shroud here to deflect rocks and to improve the draw-through vacuum effect):