check balls left out or installed where they are not needed.
leaky accumilator pistons, worn pins , worn pistons, scuffed walls of the accumilator bore, old style pistons and seals re-used
cut lip seals, lip seals left out.
Trash in the valve body area causing a cross leak , a leak in the governor circuit..... all can pioint to problems.
What I do not understand is this; You say 2nd gear applies, you touch the throttle it jumps to first with clunk. It sounds like the forward clutch does not apply initially.
If the forward clutch is applied and the band... the tranny is in second gear as it sits still. When throttle is applied IF the band comes off, there should be no 'clunk' if the gear train is loaded with the forward clutch applied. This leads me to think the forward clutch is not applied. just an idea without seeing the vehicle.
Forward clutch is applied in all forward gears... I am sure you know this, others reading may not know. When you move the shifter to "OD" at a full stop... the forward clutch applies..... you are in first gear
A bind up in OD would involve another clutch pack applied that should be OFF.
in OVer drive; The band is applied, 3-4 clutches applied, forward clutch pack applied.
If the over runs are applied during OD ... they burn.
IF the low/reverse are applied during OD... they burn
Yesterday is history.