when i claim a gamestage my game freezes/lags very bad. i dont know wat to do to fix this. after a while when the items get loaded the game returns to normal or it kicks me out of the single player game without a crash

This is likely an issue with the specific pack that you are playing. GameStages barely runs any code when a stage is granted. Large packs like SevTech have a lot of stuff going on which can cause lag though.

its in my custom modpack when i claim the quest that gives all the stages it freezes for a bit if all the gamestages are given at once you will crash

Can you upload the crash log file?

it crashes you out of single player i dont think i have them anymore if they did create a log