V7 or V8 should not make any difference in editing.

There are other considerations:
to get a firm 1->2 shift you need the Corvette 2nd servo or the Sonnax 2nd Super Hold servo, and the wider 2nd band;
you have to make sure the 3-4 clutch is not slipping;
you have to make sure line pressure is good (the pressure regulator has not worn its bore);
do you have a stall converter...?
what state is the trans fluid (color/smell/level)...?

Do you do a cal-only flash or a full flash...?
Did it flash successfully...?
After flashing, if you read back the tune from the PCM, does it compare to what you flashed in...?