I assume you have PSEN and RD anded together at 8000H so the program can run anyway. You need to make sure that the program does NOT resize external RAM when it boots up. NVRAM just looks like anyother kind of RAM and BASIC will just happily read over it and erase your program.

There are various types of programming options available when you use EPROM instead of RAM that set the first few locations in your NVRAM or ROM with the MTOP information that the code needs and also that you want to start your first program. I cannot remember exactly what you need to set, but it is (fairly) clear in the BASIC 52 manual. You could just try using say FPROG 4 or 5 which saves your MTOP and start information.

Good Luck.
STeve