As far as I'm aware there is no mod to do this, however if you know what your doing, there are specific arguments in the launcher you can use to increase the allocated RAM and maximum usage on your PC's CPU.
Also on the question is your 4gb GPU good enough for MineCraft, the answer is yes, MineCraft defaults runs on the allocated 1024mb ( 1gb ), I wouldn't advise allocating all 4gb to your game. However if you were to allocate another gigabyte your game will run a lot smoother.
I hope this helps you, and good luck with finding a mod if that's easier for you