I also only ever got much off reds without vacuum. Are you on vacuum. It seems, at least on my reds that 3/16 gravity generated vacuum can't work because the reds are not on the hills, you need mechanical vacuum. I had mine on 27", they did well, back before I had good vacuum I never tapped any reds, only sugars.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.