Have you done a pinch or temp drop test to check your low speed setting? Most folks seem to prefer the pinch test, but I've found that only gets it in the ball park and some engines need to be closer than the pinch test will get them. If you want the best low speed setting a temp drop test is the way to go.

It's been a while since I tuned an LRP BB, but I seem to remember it having a spraybar adjustment in addition to the LS and HS needles. A spraybar out of whack can cause the same thing you are describing. If it does have a spraybar adjustment, it's kind of a PITA to get it set right if it's been moved from it's default since it's most likely been set at the factory with a flow meter so the default position is slightly different on every engine.

Also, remember that the idle speed screw is always the last adjustment you make. If it's set wrong it would cause your engine to die when you are getting close to right on the low side. Use your throttle trim to hold the engine at a slightly high idle if you are having problems with the engine dying when you adjust the low side. Once you get the low speed set right, return your trim to it's original position and set your idle speed using idle speed screw.