srikanth,

1) make sure your LCD routine has integrity, write a message that comes from ROM and ensure the routine works then move to RAM based messages,
2) access time std 8051 @ 12MHz is ~350 ns. so your problem isn't here

3) sound like you have created a 64K window into your 128K ram so be careful if you have interrupts and other asynch processes accessing RAM. A common approach is to "save" the A16 bit on process entry, set it according to your requirements, and restore A16 on exit.

regards,
p