So I set up a second monitor to check out what was going on (bearing in mind I previously had 3 monitors, so this shouldn't be an issue), and it won't go past 1001Mhz on the core and 1500 on the memory for some bizarre reason. All since Crimson.
It's only in Fallout that it seems to stutter, but then I see it's capped at 60FPS in that game (lame) so the core is going up and down constantly.
Isn't this a feature of PowerPlay or ULPS (or something like that) that reduces the clockspeed to what is needed to maintain the fps required (in your case, 60fps).
I get it in a number of games if I cap my framerate my clockspeeds reduce.
In Dota 2 using the console command I can see my clockspeeds change as I raise or lower the max fps (300fps, 60fps, 45fps, 30fps, 15fps, etc.).
If you disable VSync or increase graphics settings I'd imagine you'd see an increase in clockspeeds (assuming your clocks are set to go higher than 1001Mhz).
Maybe this was something you had disabled previously but installing the new drivers has reset it?