If they didnt seat the converter fully, the truck would have never made it onto a lot. They leak if theyre not seated, and thats if you can get the bellhousing together.
A p0740 is a torque converter lockup code, meaning something is wrong with the torque converter's lockup clutch. Sometimes this is an issue with the actual TC itself, meaning problem with the clutch. Sometimes its a problem with the hydraulic circuit in the transmission that controls the clutch. In this case it sounds like the former.
OP- even if nobody else has experienced this problem, that doesnt mean its not a common issue. TC's are a complex part, and require very specific tolerances when assembled, and sometimes the manufacturer doesnt quite get all of them to spec and one slips into production. Dodge doesnt make the part, meaning their vendor for that particular part is to blame. Hope you get it back soon, make them give you a rental for your trouble.