Welcome to the GTA Forums Arvin !
The BEST Air Gun Forums on the Internet !!!!!! And, It's such a GREAT PLACE TO BE !!!!!!
Very nice collection you have going there ! And you have made the BEST Mod that you can make on a Gamo, the GRT-III trigger !!!!!
Accuracy problems are normally due to the wrong pellet, loose screws that hole the rifle to the stock or improper hold. Try holding the rifle firm, and place the hand that supports the for end between the the front tip of the stock and the trigger guard. Be Sure that you place supporting hand in the same place each time ! Fires five shots using the same hold, and make notes to yourself. Move your hand forward an inch, and try again, after that keep trying until you find the sweet spot. Some air rifles can be Hold Sensitive !!!
You might also want to check the inside of the muzzle break, and see if there are and marks inside made by pellets hitting the break before leaving the barrel ! It might be off center ?
If none of these help you, just send us a post, there are other causes !
And most fill their stocks with Memory Foam.
Now that you have joined our air gun family, I hope to see you here often !
Bill