4R70W Shifting Problem

I have a 94 GT with a 4R70W that the previous owner swapped from a 2003 V6 Mustang. My problem is that it is slow to shift from 2nd to 3rd. It is pretty bad when I am getting on it. It seems like a delay....mean time the engine is screaming and when it does shift, the shift is pretty soft. This happens with the OD button on or off.

I don't know what they did when they swapped from the AODE to the 4R70W, but I have read things like the trans needs 2 more clutch plates to make it V8 ready and the computer needs adjusted for the new gears and shift points. I'm still learning about this swap.

Have any of you guys encountered this problem?

Here is the numbers of the transmission in case it might help:
PKE-BC1
1R3P-7000-AA
045677
Bar Code: E-BC1 045677

Thanks for any help on this!

Thanks for the reply. I have stock rear gears, but the trans is different. I will look into setting the shift points...... now to figure the best way to do that.

The fluid is at the proper level and red, but I'm going to change it anyway. I'm going to look into the TCS and chip while I ask around at the local transmission shops and see if anyone is familiar with this swap. Thanks for the help guys. It is really appreciated!