I have a GP100 and it was not my favourite revolver, compared to my Smiths.
I had Rodger Kotanko at Dark International do a trigger job on it (I think he charged $65) and it is like a new gun and one of my favorites to shoot.
You can drive down to his place, or mail it to him. I have done both. He is quite fast, too.
Call him at 519 428-3127