I'd be glad to help.

Typically, writing to the glcd should be done as fast as you practically can. Ideally, your glcd routine needs to flip bits CS, WR, RD, A0, before you write something; it will be better to concatenate those 4 operations into one single write. It saves a few uSecs, but doing this repeatedly, you end up saving a lot. You may also consider in-lining your basic Command_Write, Data_Write operations so that the gosub-return overhead is avoided. Within those XXXX_write routines, you may save still more if you can write some optimized ASM. This can be the most frustrating, yet most gratifying exercise of getting the glcd to do your bidding.

Before trying to update large fonts, try to speed up the basic fonts to the maximum you practically can achieve.

Once you have this part working, you should consider writing-over LCD data. Erasing the screen / area and then writing will cause a flicker. Sometimes you may need to erase some section of the glcd. Try to keep that to a minimum.