I also got worse fps when I upgraded to 10 and I fixed it by switching my dxlevel in tf2 from 90 to 95. Also do what BurningSmile said.

I tested out 95:
2639 frames 22.995 seconds 114.76 fps ( 8.71 ms/f) 6.883 fps variability
It seems like dx90 is just bad. 95 and 98 are better options.

Make sure you remove -dxlevel 98 from launch options once you use it so it stops resetting your video settings and resolution every time you restart the game. It should save 98 automatically. I checked my game and it still says "DirectX v9.8" in video settings so I'm not sure why yours changed back.

Do you have any graphics commands in your autoexec (like mat_phong)? I'm not good at this sort of thing so that's all I can think of that might be causing the problem.

Disclaimer: This probably won't work for everyone (especially if you're already on 98)

I've been trying to get this game to run better on my potato computer now that MM and stuff requires dx90+, so I decided to try dx98 over dx90 (which I have been using ever since MM beta released). I hadn't tried it previously because most stuff I saw says it shouldn't make a difference. However, it SIGNIFICANTLY increased my performance.

No FPS config, Anisotropic 2x, Medium Texture Detail, everything else lowest possible (using benchmark1.dem):

dx90: 2639 frames 37.461 seconds 70.45 fps (14.20 ms/f) 4.975 fps variability

dx98: 2639 frames 23.701 seconds 111.35 fps ( 8.98 ms/f) 7.086 fps variability

That's a 59% increase in FPS just from changing dxlevel. That's the game going from essentially unplayable to mostly smooth.

Definitely worth a try if you're not running dx98 or 95 currently.

Edit: I tested out 95:
2639 frames 22.995 seconds 114.76 fps ( 8.71 ms/f) 6.883 fps variability
It seems like dx90 is just bad. 95 and 98 are better options.

Could you also say what OS you're running? I want to see if it somehow ties in with Win10 (which I have).

For the vsync go to the xbox app and disable the game DVR recording thing (second tab of settings). It forces vsync 60fps. I got Windows 10 recently as well and it hurt my performance too. Even with more fps settings I can't get the same consistent framerate I had before. I might downgrade but I'll wait a bit to see if anything improves.

If you aren't going to fix the terrible performance I would at least allow more graphics commands in MM. Making sure a portion of the playerbase is able to play at an acceptable framerate is more important than maybe a few people seeing TF2 on twitch with bad graphics and not installing a FREE game because of it (even though anyone with a brain could spend 2 minutes and find out that there are different graphics settings).

This is my biggest beef. I've had to work around the bad performance in this game with configs, and now they've restricted configs without actually fixing the underlying problem of the game running terribly. If you're not gonna fix your game at least allow me to run it properly by modifying it.

I recently did a clean reinstall of this game to see if it would help my issues but I'm pretty sure my framerate is somehow even worse now.

2639 frames 29.505 seconds 89.44 fps (11.18 ms/f) 5.254 fps variability
2639 frames 40.645 seconds 64.93 fps (15.40 ms/f) 4.321 fps variability
Texture detail low vs medium (as locked by mm) thanks valve

CPU and overclock: Intel Core i7-3630QM CPU @ 2.40 GHz
Graphics Card: Intel HD Graphics 4000 (lol)

dxlevel: 90
Resolution: 1024x768
Full-screen or windowed: Full
FPS configs enabled: no
Shadows enabled/disabled: disabled

Additional notes: I basically have everything as low as possible without using a cfg (I had one for a while but I removed it after mym)

Try going to steam -> settings -> in game and change server browser pings/min to a lower number than 4000 (like 500).
The rest of my post doesn't matter but you can read it if you want.
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There's an option to reduce how fast you send requests to servers in steam. If you ping too fast it denies access because it thinks your ddosing it or something. The option somewhere in steam and it helped me when I couldn't connect to Virginia servers. The default is 4000 I think and I reduced it to 500 maybe? It was a while ago I don't really remember the specifics.

Sorry for the vague response but hopefully you can find the setting and change it. It's in steam not tf2.

Edit: I found the thread I used to fix the problem initially (it's a slightly different problem then yours but I wouldn't be surprised if it has the same solution)
http://steamcommunity.com/app/440/discussions/0/620713633847476540/

I visited Yellowstone for a second time in 2014 and it's extraordinary. The geysers are amazing and the scenery is gorgeous. It's my favorite place to visit in the U.S.

Here's some of the pictures I took. It definitely doesn't do it justice, but it'll give you an idea of what it's like.
http://imgur.com/a/ahZpt

I watched 5 seconds and knew I didn't need to watch the rest of the video

Looking forward to machete spy

It says 90 even though I thought I set it to 95 a few days ago.

And yeah, getting rid of my fps config did seem to help. I played a classic game of 6s swiftwater and didn't get fps drops as often, and I could tell I was idling at a higher framerate. It's not as good as dx8 but it's definitely better than it was before.

I'll check it out

On dx8 I could easily get 100 fps at essentially all times, but now with the forced settings for MM I hover around 50 when nothing is happening and dip down to ~20 during fights. When I was playing snakewater I got sub 20 fps almost the entire game. I can't aim properly. My computer is pretty bad but I wouldn't think that I should get 20% of the fps I was getting before just because of dx9. I even turned on sillygibs and it didn't really help.

Is anyone else having this problem/ know anything to try to at least make this game playable again?

This is me when I'm not running gunboats

I sometimes try to rocket jump with a sniper rifle too when I'm not paying attention. I might have a disease