1972 Chevy Chevelle Fluid leak

Transmission problem
1972 Chevy Chevelle V8 Automatic

72 turbo 350, is there an overflow if overfilled? Serviced the trans, fluid, filter and modulator valve, deep B & M pan, drained about a gallon out, 6 qts added but barley showing on dip stick. Trail of fluid when driven and small puddle under front left corner of pan (looking from front of car). Was using fluid before, bad mod valve.