Only time I had a problem with a converter locking up was on a Ford E350 chassis for a Motor Home. All that needed was a change of the trans oil and filer. Might be worth a shot, although I know the AW4 is totally electronically controlled.
There are numerous forum discussions about modifying your trans for total manual control, while retaining the auto mode.
Having said that, are you sure that your whole problem isn't related to a bad electrical connection either at the trans or at the shifter ?