I own a EVGA GT 730 2GB GDDR5 graphics card and I have it overclocked to 1137 mhz on the core clock from the stock 901 and the overclock works just fine in other games, yet tf2 is the only game where it underclocks itself to normally 732 mhz when in a game but it usually fluctates from anywhere between 732 to very rarely 1137. It will be at a constant 732 and then suddenly change to the 800s or 900s, which results in framedrops. The only reason I can think why it doesn't run at the overclock is because tf2 isn't a very demanding game, but I have no idea why it tends to fluctuate in mhz. I already use a config but even then my fps can drop to the 20s with the low clock speeds, so I think if I could have it play at a constant 1137 mhz I would have no issues. I've already tried removing the overclock but even then it will go underneath the stock 901 so I'm not sure what else to do. I'm using MSI Afterburner to monitor the graphics card and fps and it's also the program I used to overclock in the first place. Also as a side note the gpu is at 1137 while just staring at the main menu screen, but when I go into a game then it drops to 732 mhz and goes up and down from there.
 Found a better solution that it just being my cpu, since that really didn't have anything to do with my graphics card underclock itself. What I did was change power management mode to perfer maximum performance in nvidia control panel in 3d settings. Now it runs at a constant 901 MHZ (stock w/out overclock), which is still better than it fluctuating and going under stock clock speeds.