What’s up with this

Ok so I have a 02 yukon xl 5.3. The
cam shaft sensor has read low
voltage code so it’s been gone thru
literally everything has been tested
out sensor is good the sensor wheel
seems to be working right there is no
breakage or resistance in wiring.
Was even told to
Replace ecm I did dealer did that but
that ecm has never worked right they
wanted to reprogram said it didn’t
take but was gonna charge me again
not happening I put old ecm in
works fine drive all day long no
codes turn it off  then when you
restart a min later or even next day
code thrown again battery tested ok
but I’ve seen battery’s test out and
still have a dead cell could that be
the problem sick of dealing with
shops sick of dealing with same
issue for months not getting
anywhere