You should improve yield by giving adequate root space. Don't try to slow root growth; you need a healthy root system. There's a good chance your yellowing is caused by teh rootbound condition- a rootbound plant will show def symptoms even if the pH is correct and you are feeding properly. Do all the plants since they should all be behaving similarly.
Cutting veg time down isn't a bad idea next time around, and neither is 5 gallon pots. IT depends on what you want to end up with in terms of plant count.