Tested on Fallout 4 and I hit the 144pfs (monitor limit).
Fallout 76 is always at 48fps regardless of where I am in the world (outside or inside) or what I am looking at (sky or ground).
Sounds like the issue of playing that game in bordered, borderless windows mode.
And also remember to check monitor refreshrate after changing GPU. It might be defaulted to 60Hz.
It was running in a borderless window. Changed to full screen and FPS went to 72. Primary problem was FO76's poorly implemented (or bugged) VSYNC. Added (changed) "iPresentInterval=0" to my Fallout76Prefs.ini file and the frame limits went away
That's crazy...I average 100 FPS on high settings on and AMD RX 480 8 Gb. I do play at 1080p, as that's what my TV will support. I did run into this myself, and it turned out to be the tweaked ini settings that I obtained from guides that were making the game unplayable for me. I reverted to defaults within the game and it made the game better looking, better performing and buttery smooth. Unless the server is busy of course.
Got to Fallout76Prefs.ini (My docs>My Games>Fallout 76) and set "iPresentInterval=1" to "iPresentInterval=0" (1 = vsync on ; 0 = vsync off) under the [Display] field.
Oh yeah, and I get 100 FPS in borderless window mode. I've learned the hard way not to listen to everything people say on the internet. They never let facts interfere with their opinions. Test it out for yourself.