Hey Brian,
Great to see you back on the forum! I had a similar experience with AutoMeter and a tach - went south, reading funky and they "fixed" it for $25 plus $12 shipping. Had it back about two weeks and it went erratic again. Contacted them, decided to invest the $5 USPS charge to send it to them again and they replaced it as a warranty claim, though it was clearly out of the time window. Good guys & gals at AutoMeter.