ncis350z

my 350 z was in the shop for over 3 months. nissan could not find what is wrong with it. they put in a rebuilt trans, took out my jwt clutch pressure plate and fly wheel. This was put back in after it did not solve the problem. they replaced mass airflow sensor, modual to the abs, rear left abs sensor, new spark plugs, fuel system cleaned and drained twice. took off and put back on my 20 inch tires. they thought the size and difference in tires would have been the problem but it was not. after 3 months they told me they do not know what to do with it and to take it to a speed shop and have the ecu redone. I did research on this site and thought the knox sensor and wire was the problem. so i took it in to be replaced, and all that did was cost me $710.00. did not fix the problem.

The problem is on cold start ups and on damp rainy days, the car has no power after 35-4000 rpms. when its warm it runs great. when its wet and rainy or cold, the car does not gain power. any input would be helpful. im not sure where to go from here. i have more information to offer if anyone has questions.

thanks for any and all help.