BL3 requires considerably more horsepower than BL2 to run nicely, it ostensibly looks quite similar as it has the same art style, but the engine is doing a lot more fancy stuff. (Plus they moved to Unreal Engine 4 for BL3, which is a modern, demanding game engine.)
My PC isn't ninja cutting edge now but it was very nicely specced when I bought it back in September 2017, and it has a GTX1080 graphics card in it. Running the game at 1080p with a mix of High/Medium detail settings is about my lot if I want to keep it at the sweet spot of 60FPS (and even then it drops quite a few frames when things really kick off). (My screen is 4K but I can't even remotely run the game at that resolution and get a decent framerate.)
Like you mack I can't play FPS games with a gamepad at all, so I need my keyboard and mouse for games like BL3!
Did you get the expansions for BL2? The base game is fantastic but it also has four amazing expansions.
I've just had a look on Epic and the BL2 Handsome Collection is currently on sale, so £12.49p gets you all the BL2 expansions and other extra content, along with Borderlands The Pre-Sequel and all its extras too - that's a lot of stuff for not much more than a tenner!
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