Hello,
First time replier. Long time LB lover! I breed purely LB's and we had the same problems when we started. They are good doers for sure. I abide by the 20 minute rule and feed an Allen and Page rare breed feed (pricey!). Nowadays we have really consistent fat levels. I think it is as much about getting your eye in as it is changing feeds etc. Mine go at 5-6 months and I watch them like hawks for the last couple. If you are grazing them or they have good rooting it will go a surprisingly long way! Definitely bring the protein levels down if possible. Remember that non traditional breeds are sometimes expected to make weight in half the time.