I have a horizontal line across my R & G tubes and a slight one on my B tube on my sony vph1000Q. Is this a failing tube issue or do I just need to adjust my H/V settings?

Is the line at the top of the image or in it somewhere?

it is directly in the center of the crt tube screen

Try moving the picture up or down, if the line moves with the picture it's not
bad. The 10 series are known for having a line when the convergence is getting maxed out. try centering every thing and reconverge.

No, this line is on the crt screen when the machine is off too. I've tried everything to get rid of it. Could something have been burned into the phosphurs? Should I just junk this behemouth?

Yes, a line has been burned into the tubes somehow. Good red tubes are dirt cheap, greens are a bit more. But yeah, at this point I'd look for a data grade set.

"Should I just junk this behemouth?"

For the price of a fix, you could move up to an even larger behemouth!