My Buick had stalled occasionally while driving when cold and I would pull over and restart it. i did a full tune up and replaced the fuel filter also. I noticed when when i gave it a lot of gas to check it stuttered and then smoothed out when I let up on the gas. While pulling out of parking lot, it stalled and would not start. It was towed to shop and I have replaced the crankshaft position sensor, ignition module, the ecu, and checked for spark as well as fuel pressure. there r no codes to be read. It starts and isles fine but now it stalls out when given gas. It stalls whether it is in park or drive but if u give it gas easily it is OK. It has been in 2 shops for 3 weeks. Is there anything else I am missing?