More information needed:
Update your post to include full system hardware specs and OS information.
Include PSU - make, model, wattage, age, condition (original to build, new, used, refurbished)? History of heavy gaming use?
Disk drives: make, model, capacity, how full?
Download speeds
Network: make and model information for modem, router (or modem/router if combined)? ISP?
Are any other computers experiencing drops in download speeds?
Crashes
What games are you playing?
What apps are running in the background?
For now (and there are other ways to look) look in Reliability History for error codes, warnings, or even informational events being captured just before or at the time of the gpu crashes.
As an opening thought, my first suspect would be the PSU. TBD.