Pixelated / blurry stream on Rocket League, split second fps drops while streaming.

[MendoXen]

System:

GPU - gtx 1060 6gb
CPU - Ryzen 5 2600
RAM - 8GB DDR4 3000Mhz
STORAGE - 120 Gb SSD and 1Tb HDD

Streamlabs OBS settings:

Output res - 720p
Downscale filter - Bicubic
FPS - 60
Bitrate - 6000 (I am affiliate)
Encoder x264
Encoder preset - very fast
Process ppriority - high

Problem:

Playing with this system is amazing. If I am not streaming, i can get 250+ fps on rocket league if I do not cap it (which I do cap it at 144 fps cuz thats my monitors refresh rate). However, when streaming, the fps dips below that 144 cap AND sometimes i get random anoying hitches (fps drop to around 90 for a split second or something) and its very noticeable. also, these lags happen on other games too sometimes but mostly on rocket league.

Problem 2:

I tried streaming a few games: Fortnite, CS: GO, Rocket League, Osu!. Out of all these rocket league looks the worst, compared to Fortnite, it doesnt look as smooth and it looks pixelated or a little blurry i dont know how to explain it. Here are clips so you could see for your self:
Rocket League: https://clips.twitch.tv/SpineyJazzyGrouseBrokeBack
Fortnite: https://clips.twitch.tv/LongClumsyLeopardSaltBae
CS:GO: https://clips.twitch.tv/RudeDependableTitanBabyRage

What I tried to change:

Played around with bitrate
Tried different downscale filters
Tried different encoder presets: 1st i tried streaming with "fast" and "faster" presets and i thought maybe my cpu cannot handle this and its causing those sudden split second fps drops that look like hitches but it happens even on "very fast" preset.