Transducer installed under engine... Is not accurate (only in the deep). Otherwise, bad readings, flashing numbers 90% of the times. Was installed by dealer, he offers installing a new transducer outside on the bottom transom... (62 MPH boat)

Any suggestions ?

Was the hull hole sawed out to the outer skin? DId they put mineral oil in the cavity?

I wouldn't go external.

Some have sensitivity adjustment on the back of the gauge.
My "UNIDEN" did. Once adjusted, alway's had good reading.
That was in a CHECKMATE with a balsa core hull. I didn't get down to the outer skin and it worked fine.