unstable fps under heavy loads

sabzi

I got aspire v15 nitro(vn7-593g), it showed some graphical issues and I thought it is from the paste, so I tried to repaste and I was right, the paste was totally dried in 1 year. I repasted the gpu and put everything back, but the problem is now I have very unstable frame rate when my gpu is under heavy load or running heavy games and its not just the normal drop. For example I play The Crew2, my average fps was 40 in the benchmark mode of the game, it is still 40 in the benchmark but in the game, it starts with 40, then goes unstable and goes to 20, then back up to 45, then drop to 30 and on and on. it does not have a routine but all of those fps are so unstable and changes so much every 2 or 3 seconds. like im on 45 fps for 2 seconds, then dropped to 20 for another 2 seconds.
should I repaste it again or my gpu might be damaged due to heat?
also I didn't have any fps issue before the paste run dry