I was also using molasses but i'm not sure if thats the problem. I re-potted when i switched to flowering and currently my pH is about 5.8-6.5.
I thought molasses was good for preventing nutrient lock out but from what people have told me on this site and from what i've read, the yellowing of the leaves seems to be a nitrogen deficiency. I have been using nutes but, the nitrogen deficiency could be caused by a nitrogen lock out. Thats why i flushed my plants in order to clear out any salts or build up that could be causing the lockout.
I'm not sure if this will fix the problem but i figure this is the best start to isolating the problem.
If anyone else has suggestions, i'm sure many on this thread would appreciate it.