<VV> PG problems

[Eddie MEADOWS]

Working on an 8/10 Cord that has a Corvair 140/PG powertrain.  Car has not run much in the last couple of years.  PG will slips like it does not have enough tranny fluid (has correct amount in sump) when starting up in drive and then slips when going from low to high.  Put it in low to start and there is no slippage and does not slip when then putting selector in drive to let if shift to high.  Is this an adjustment or rebuild time? 
 
Eddie Meadows