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That does not sound right. the shunt should be around .5ma on full raster, too about 1.5ma full dark. I suspect your are not reading something right or your meter is not working correctly if you are seeing 5ma
you need to put the HV meter on the CRT, put the current meter in the jumper and watch the HV vs Shunt tube current as you adj the brightness on a raster.
Set the HV pot for 24kv then adj the bright up and down note the shunt current, if it goes up as the crt goes dark and goes down as the crt brightness increases, then the shunt is working as it should.
If the above is correct (shunt working as it should) then you need to go back and recheck the HV setup, starting with the cathode current dip on the eff coil.
when you get all that sorted out and have the correct meter readings (.5-1.5ma shunt). Then you can restart the trouble shooting. One other thing, assuming the HV is ok is the focus voltage can cause what looks like blooming including complete darkness on the CRT. The pin and or the socket at the CRT sometimes fails from corrosion.
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