Delayed 2-3 upshift 4 cyl auto transmission

1991 Voyager with 3 speed automatic transmission, began gradually having a delay in the 2-3 upshift. Initially, was minor and only occurred cold. With tranny warm, all shifting was fine. Gradually became more severe, but still only on the 2-3 upshift. Have removed transmission, reconditioned the valve body, removed and checked the governor valve(s). Had some slight burring of the valve body transfer plate at one check ball. Front and rear clutches can be actuated with air pressure, fluid shows no sign of metal contamination. Bands do not visibly show wear (viewed with valve body removed). Am currently making a holding bar to remove the transfer gear and check the governor support seal(s). Anyone with any advice on what else to look at? I have not yet decided whether to completely rebuild the transmission (at this point have not removed the oil pump, planetary gears, etc).