FC 45

[Matt S Bower]

Hey guys,  I could use some advice on this.  I have a 93 s10 blazer with
cpi.  It's setting a fualt 45.  Using the scan tool I am seeing that
when I cruize at highway speeds the O2 sensor voltage will hold at .85
volts and after a couple of minutes it will set the code and kick it out
of closed loop.  It then holds O2 volts at .92 and will stay usually
until I go back to start stop driving at which point the ecm goes back
to closed loop and the O2 sensor starts swinging from .1 to .8 volts. 
Any ideas as to what I am not seeing here?

Thanks Matt.