game froze again after ~20minutes. using the 20130725 version firmware. so if downgrading to 20130725 fixes TF2 it likely isn't the same issue as TF2.
game: stellaris

commands run to downgrade to linux-firmware-20130725:
sudo pacman -U /var/cache/pacman/pkg/linux-firmware-20130725-1-any.pkg.tar.xz
sudo pacman -S linux

other info:
Name            : llvm-libs
Version         : 3.8.1-1
Name            : linux
Version         : 4.7.2-1
Name            : mesa-git
Version         : 84594.98f734e-1
Name            : linux-firmware
Version         : 20130725-1

lspci:
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Oland XT [Radeon HD 8670 / R7 250/350]
01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde/Pitcairn HDMI Audio [Radeon HD 7700/7800 Series]

boot logs:
Sep 04 11:12:28 jambli kernel: [drm] initializing kernel modesetting (OLAND 0x1002:0x6610 0x174B:0xE269 0x00).
Sep 04 11:12:28 jambli kernel: [drm] register mmio base: 0xFDD80000
Sep 04 11:12:28 jambli kernel: [drm] register mmio size: 262144
Sep 04 11:12:28 jambli kernel: ATOM BIOS: C66201
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: VRAM: 2048M 0x0000000000000000 - 0x000000007FFFFFFF (2048M used)
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: GTT: 2048M 0x0000000080000000 - 0x00000000FFFFFFFF
Sep 04 11:12:28 jambli kernel: [drm] Detected VRAM RAM=2048M, BAR=256M
Sep 04 11:12:28 jambli kernel: [drm] RAM width 128bits DDR
Sep 04 11:12:28 jambli kernel: [TTM] Zone  kernel: Available graphics memory: 8209378 kiB
Sep 04 11:12:28 jambli kernel: [TTM] Zone   dma32: Available graphics memory: 2097152 kiB
Sep 04 11:12:28 jambli kernel: [TTM] Initializing pool allocator
Sep 04 11:12:28 jambli kernel: [TTM] Initializing DMA pool allocator
Sep 04 11:12:28 jambli kernel: [drm] radeon: 2048M of VRAM memory ready
Sep 04 11:12:28 jambli kernel: [drm] radeon: 2048M of GTT memory ready.
Sep 04 11:12:28 jambli kernel: [drm] Loading oland Microcode
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: Direct firmware load for radeon/oland_pfp.bin failed with error -2
Sep 04 11:12:28 jambli systemd[1]: Created slice system-lvm2\x2dpvscan.slice.
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: Direct firmware load for radeon/oland_me.bin failed with error -2
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: Direct firmware load for radeon/oland_ce.bin failed with error -2
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: Direct firmware load for radeon/oland_rlc.bin failed with error -2
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: Direct firmware load for radeon/oland_mc.bin failed with error -2
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: Direct firmware load for radeon/OLAND_mc2.bin failed with error -2
Sep 04 11:12:28 jambli kernel: [drm] radeon/OLAND_mc.bin: 31452 bytes
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: Direct firmware load for radeon/oland_smc.bin failed with error -2
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: Direct firmware load for radeon/OLAND_smc.bin failed with error -2
Sep 04 11:12:28 jambli kernel: smc: error loading firmware "radeon/OLAND_smc.bin"
Sep 04 11:12:28 jambli kernel: [drm] Internal thermal controller with fan control
Sep 04 11:12:28 jambli kernel: [drm] radeon: power management initialized
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: Direct firmware load for radeon/TAHITI_vce.bin failed with error -2
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: radeon_vce: Can't load firmware "radeon/TAHITI_vce.bin"
Sep 04 11:12:28 jambli kernel: radeon 0000:01:00.0: failed VCE (-2) init.