when raining kind of heavy car 2004 grandprix slows down to 45 and cannot get it to speed up unless put the pedal to the floor when rain slows /stops starts working again within a minute or so anyone had this issue before

Are you getting a Service Engine Soon (SES) light come on? Have you connected a scan tool to your OBD II port to see if you have any stored trouble codes stored in the computer? 

Off the cuff - a dirty fuel filter can cause problems you are describing. Pontiac uses inline fuel filter canisters than run underneath the driver's side of the car.

Another possibility is that rain / moisture is getting into the ECU/PCM module under the dash and setting the car into "safe mode" or sometimes call "limp mode".

Another possibility is you have a bad throttle body assembly and/or throttle position sensor.

Another possibility is the gas pedal may need to be replaced since the car is drive by wire.

These are all possible causes. I would start with the scanning the computer to see if you have any error codes. If you do address them first.

no codes stored, no service engine light when not 100 outside going see if can make it happen with water hose had light rain yesterday and was fine

 

I would consider replacing the fuel filter and removing the  throttle body assembly, thoroughly cleaning it, replacing the gasket. Next look to see if you are getting water in or around the ECU. Look at a new pedal last. 

Also check you air filter box. Is the filter getting saturated with water for some reason?