First I'd take it back to the shop and say WTF!?!? I'm sure all that work wasn't cheap! If it's a decent shop they should have figured out what the original problem was, unless they changed a whole bunch of sh*t for no reason just to bump the bill. (sounds like you and I have the same stamp on our foreheads that says "please screw me".....

) Anyway, to me it sounds like it's more in the trans, not the primary drive. Maybe your clutch isn't engaging all the way or something like that. Sorry, that's about all I can offer. I'm sure someone else has a better idea to offer up.