GPU usage and CORE CLOCK fluctuating!

In AMD control panel, Under Global, turn power management OFF.

That will stop clocks dropping, UNLESS you have framerate cap set in which case once you hit that, clocks will drop as usage drops.

You need that latest Crimson drivers

Ok when you say dropping....my core clock is never at 1100 even when pushed hard. It'd like 1100/1098/1097/1101 etc. Which is fine. Gpu usage drops indicate throttling due to thermals, bottlenecks, game code being terrible or drivers.

What are your temps when Ir happens? Cpu usage? Ram.usage?

You got the msi app installed? That will mess with afterburner!

You really must use the newest crimson drivers. Turn off frtc and power management. Works fine with mine. Which games by the way?

Issue :
1. There is throttling kinda issue for GPU usage, GPU clocks
2. Similar issue will be with corresponding Memory [obviously]

Solution [Partially Tested] : [if you have played with driver installation and uninstallation as AMD driver installation have lot of minor to critical issues if not blockers like AMD Radeon Setting not installed even though user has installed them]
1. Use AMD utility [amdcleanuputility or DDU] and clean everything
2. Restart PC. If you have any other "sensor polling" application like HWInfo or monitor other than Intel Extreme Utility uninstall them here in this step. This include factory apps of MSI/ASus/whosoever [ex : MSI afterburner, MSI Gaming app , Tweak II or Trixx]
MSI Gaming app, you just dont install this there is no issue with app but creates issue for others and card. [scarcely read on guru3d but ignore my claim here as I am not sure per se if it was on guru3d or somewhere else]
3. Restart machine.
4. Use AMD autodetect utility or if you have latest in your hand install them now here.
5. Install Tweak II or afterburner or whichever
6. restart machine , You should not have any issues now. Hoping #1 and #2 went well.

Solution 2 [Tested] :
1. If newly card is installed in rig. just make sure that you install drivers [obviously old] from DVD which came In-Box.
2. Once installed update through application.

Solution 3 [Untested] : [If you have Win 10]
1. Install card in rig and do not install any drivers
2. Let Win 10 pick it up , just visit Windows Update center and click check updates now.
3. Install Afterburner/Tweak II or whichever.

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Once installed from one of the solutions from above, use afterburner/wattman or tweak to increase power limit to +5/+10 ideally step size of 3 would suffice instead of 5. Try this with steps of +1 on power limit if you want to be very cautious.
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NOTICE : It is expected of you to make sure that machine is at "ground-zero" i.e it is void/clean of any graphics drivers , that may be stale intel HD, previously owned cards of AMD/nVidia or related. try to avoid formatting of HDD and install-reinstall OS. It may or may not work. If it works fair enough Just-In-Case if it did not , your efforts and time both in vain.

Note : Not every latest drivers will give solution, stick to 'stable" release while doing installation in above steps.