oil pan
Mine runs low 13's easily and would break into the 12's if I had enough traction and never shows signs of oil pressure drop with a stock pan. I know every application is different but you usually don't need any extra capacity pan for a low 15 car. I'm thinking like Rumble that either you don't have enough oil in it or possibly the pickup is too far off the pan floor. The Kevco pan is a real nice unit and nearly impossible to beat on price. You could also weld a rear baffle in your stock pan.