I have a NZXT Gamma case, its a mid tower. Im definitely going to clean the dust too and create more space for more airflow. Would adding more fans be fine as well? The case only came with 1 unfortunately.
If you clean out the dust and then your temps come back to normal then that is the fix for that. If the dust removal doesnt help with temps going back to cooler territory then I would first check into either applying new thermal compound or replacing the stock heatsink with a better heat sink and applying new thermal compound.
If you have a tube of thermal compound, I would with computer off carefully remove the heatsink, then use Q-tips to carefully remove the old thermal compound from the CPU surface and the heat sink surface so they are clean again and ready for new thermal compound. Then apply new thermal compound such as a drop of it at center of the CPU and apply the heatsink down onto that drop of thermal compound, or apply the thermal compound evenly across the entire CPU metal heatsink surface with a toothpick as I like to do to make sure that the entire area of the CPU bonds thermally with the heatsink surface when the heatsink is applied.
Then if you didnt replace the heatsink and the thermal compound brought your temps down, then you are all set; however if this does not fix the problem then you would want to replace the heatsink with a better heat sink.
*** One way that a CPU can roast even with adequate thermal compound with a stock heatsink is if you are overclocking the CPU at all. If you have any overclocking set for this CPU with a stock heat sink, I would set the clock back to native clock and see where that places your CPU temp. I have seen some people set an overclock to a CPU with stock heat sink and roast the CPU because they really need to replace the stock heatsink with either a better heatsink with heat pipes or even better liquid cooling to draw the heat away as fast as possible.
Also a properly cooled CPU would drop in temperature very quickly vs slowly, and so I think you have an issue with the heatsink not able to draw the heat away effectively.
My older gaming system I have a 10% overclock on to turn a 2.3Ghz CPU into a 2.53Ghz CPU by changing my FSB speed from 200mhz to 220mhz. Prior to applying new thermal compound, my CPU when hitting windows key out of a game back to desktop from Windows 7 64-bit would slowly drop in temp. I removed the heatsink and replaced the older white now semi dry semi wet thermal compound with new Arctic Silver thermal compound with the same stock heatsink, and now when pressing the windows key to get back to desktop from a game such as World of Warcraft my temp drops from 52C to 41C within like 5 seconds. Prior to applying new thermal compound It was dropping slowly taking almost 15 seconds to get back down from 52C to 41C which is the idle temp when the system is warm and running idle. If I set my clock back to 2300Mhz from 2530Mhz I can drop my temp by 5 degrees and go from a max temp of 47C to an idle temp of 36C. But the overclock makes for some excess heat all the time.
If you want to test to see if you need more case fans you can run the system with the side panel off so the box can breathe and see if the temps stay cool with the side panel off. If the temps are all much cooler then you know that you need to add more fans to the case. These can be added by use of an unused 5.25" bay or fans that can mount the same as a card into a card slot to suck the warm air out of the inside of the case and blowing it outside the case at the rear of the computer. ( * Note: These slot fans work good, but because of their location in the case they are usually pulling air from the middle or bottom of the case, when the warmest of air would be at the top of the inside of the case. So they can help, but arent as efficient as a fan that is in an 5.25" bay which on a tower is towards the top on most systems where the air is warmest. )