Are you using the GRT EIS for your sensors? It then transmits the readings for display in the EFIS.
I have that setup, and when my Princeton fuel senders went bad and caused a short, all the OTHER sensor values went crazy. For example, my voltage reading showed 24v even though it was 12v. CHTs and EGTs also showed values out of range.
The correlation with transmitting only is interesting, but my guess is some kind of short somewhere-- probably involving the radio/antenna or PTT.
Clay R- RV9A - Flying since 2004 - 400 hours
VAF dues paid through end of 2020.