Driving an LCD is a slow business. It's best to do your A/D conversion, then format the data in a buffer, then send the whole lot over to the LCD as text every so often (16Hz is fast enough for us humans!). Don't forget the timing involved! Driving the LCD too fast causes missed characters & control codes. Clearing the LCD can take 10's of mS! If possible, use the LCD's status bit to get maximum speed.
I've done a few projects in assembler using LCD's, & they've never been too much hassle (except when grabbing LCD data for other purposes, but that's another story).
Keep trying - *never* give up! Hardware & software will *always* work in the long run! (who just said "Windows"?).

Regards,

Richard