We map a LOT of Bm's. Probably more than VW's infact.
Which model 320d coupe do you have? Which engine version? (150hp - 163hp - 177hp)
We are tuning a BMW 2.0d engine thats competing in thus years BTCC and the later 2.0d engines are good for 240+ bhp with the stock turbo. We have 2 320d's ourselfes which are both mechanically standard the first is a 150hp e46 which makes 207bhp and the other is a e90 163hp which makes 221hp so dont dismiss the 2.0d engine, its a very tunable and capable unit.
Superchips, dont bother as you have found out they simply dont have tne ability to map for the complex auto box, it often becomes jerky with odd shift points, is this what you discovered?
Our own BMW tech has 20+ years of tuning and now runs a dedicated BMW tuning outlet, if you want some free help or advice just give us a call.