did u flush the cooler lines during the trans swap? is the 700r4 rebuilt?
another thing that can cause a no upshift condition is a broken or "applecored" govenor gear.
lastly, u mentioned that the car is a buick regal, has a engine swap to a chevy been done? a 700r4 wont bolt up to a buick engine. r u sure its not a 2004r?