GMP4 ECM '89 HELP?!?

[Dave Zug]

hello, i'm new.. heres the short version of my quest:

I have an 89 pontiac grand prix turbo 3.1L. it uses a GMP4 ECM and i 
have been trying to modify the "usual parameters" as it is called in one 
of the messages i read in the archives of this mailing list..the spark 
advance, the injector tables, the turbo boost limit, fans, TCC lockup 
... ... ...  Anyway, i have READ the prom, and can see tables(though i 
dont know which is which), i can burn a duplicate chip (its a 27c256, 
mounted in the mem-cal next to the ELECTRONIC SPARK CONTROL module) but 
every chip i burn with even one value changed, causes the ecm to go into 
"limp home" mode i think.  i beleice the checksum has something to do 
with it, but i dont know where the checksum is! i dont know how i'll 
ever find the 15 pound boost limit setting, or find out which table is 
what unless i can make subtle changes and burn a chip..the checksum is 
keeping me from doing that! for info: the grand national 3.8L turbo and 
the TTA 3.8L turbo use different ECM's with 4k eeproms, my ECM is a 
different type. what i guess i need is to fing the original programmer 
and get him to give me all the data he has! yea right.  any help would 
be great  thanks!