1993 Ford Aerostar shifting

I guess what I gotta ask first is ARE YOU SURE THAT THE FLUID AND FILTER got changed. Yes it does sound like a pressure problem but normally a pressure problem shows up AFTER warmup and not the other way arround. Unless the filter is plugged and not letting the Colder THICKER fluid pass through a partiall plugged filter. The potential pressure problem will become worse after warnup as the fluid heats and gets thinner and harder to hold into worn or cracked seals and clutch packs.
Get an auto parts store scan to check for possible CTS or Trans temp codes and get back w/Me Larry