No Forward Gears

Fluid level and condition, shift linkage, low forward clutch pressure, low line pressure, filter (plugged or damaged), valve body (3-4 shift valve, main regulator valve, manual valve stuck or damaged), incorrectly tightened valve body bolts, valve body gaskets damaged, 2-3 accumulator, pump assembly, forward clutch assembly, low one-way clutch assembly (planetary) or output shaft.