Lag With Higher Screen Size/Resolution

My game runs flawlessly.. on 1920 x 1080 screen size/resolution. All high settings (except I keep lot distance low.) But I'm trying to use a 70 inch monitor. The size is 3840 x 2160 4k res. The moment I switch to 2560 x 1440.. slow down. 3840 x 2160?.. MEGA lag. What is the problem? I've tried lower settings to medium or low.. no difference. I've tried windowed mode, no difference. I'll share my specs and mods below. Do I need a PC with higher specs than what I have? Can you spot what is causing my issue and provide any ways I can fix?

Here's my SPECS: Processor Intel(R) Core(TM) i5-7500 CPU @ 3.40GHz (3.41 GHz), RAM 16.0 GB (15.9 GB usable), NVIDIA GeForce GT 1030 (2 GB), Intel(R) HD Graphics 630 (128 MB), Storage 98 GB of 1.14 TB used, System type 64-bit operating system, x64-based processor

MODS: TS3 GPU Add-On (to recognize graphics card. It's working.. 1 found 1 matched.), Lazy Duchess Smooth Patch, Memory Modder (reduce memories), ErrorTrap, Master Controller, Overwatch (with all cleanups on a timer), Tiny UI Fix (as needed depending on screen size)

The lagging at high res begins at the immediate load up screen of the game. The lag is so bad that any mouse movement has a 4 second delay 😳 (corrected instantly by switching to lower screen size)

Please help