Minecraft with mods?

So I play Minecraft with the following mods: Advent of Ascension and Twilight Forest. My graphics card is a GTX 1050 TI and I have 300 FPS continuously but sometimes it just drops to 20 or so. Does anyone know why?

You could try if you haven't done that yet, take the Mod Optifine in and then look in the Graphics Options Smooth FPS and activate it, and generally screw down the graphics a little if that doesn't help.

Cool Thanks already found the problem (assigned more ram) but you reminded me to install Optifine.