running lean
 

If my only mod was a full exhaust either turbo back with a highflow cat or no cat and a midpipe, would my car run lean and would there be a need to upgrade the ecu with a chip or get a fuel computer?

The way I know it to be is if you have at the least a high flow cat than you should be fine if you controll the boost with a boost controller no higher then 10 pounds. If you run a catless then your asking for trouble if you don't upgrade the computer.

with the boost at 10 psi , with some method of controlling it other than the stock ecu, you will be fine. watch for any creep and keep an eye on the transition spike

Technically with the boost at stock levels there is no problem. But in reality with full exhaust you would get bad boost creep and/or bad boost spikes. Even some boost controllers can have a hard time dealing with that. High flow cat would be a lot safer, with a DP, MP, and CB your asking for too much boost.
Evan

profec b should handle it np.