I see it as the opposite--in ANH the Falcon is a bucket of bolts but in ESB its this graceful acrobat of the sky that can do things no other ship can. The thing about the Falcon is that it is a bucket of bolts. Thats how Solo conned Luke and Kenobi in ANH--"oh youve never heard of the Millennium Falcon? Its famous!" But then when they finally see what they expect to be a suped up racer they see this old transport truck sitting in a garage and Luke says "What a piece of junk!" Thats the joke. It's a piece of junk. But as Han says, its got it where it counts--it can do the jump to lightspeed and Han is a clever and wiley fellow. If you look at it in ANH it doesn't move impressively, it just chugs along like a truck, and it even backs out of the Death Star hanger like one (its not hard to imagine beeping sounds as it reverses). But in ESB its this amazing thing that can do acrobatics and really is an impressive ship. But thats sort of a retcon of ANH. Its just a transport freighter. It doesn't work all the time, it looks like its literally falling apart, and its probably really old and outdated but its kept around because Han's made a lot of special modifications and updates.