Is the shift delayed in auto/drive mode, manual shift mode or both?
How many front clutch springs are you using, and did you install the restrictor from the shift kit into the trans case?
What type of front band material, and is it adjusted correctly?
I would try loosening the front band adjustment about 1/4 turn first, because that would be the easiest thing to check/adjust.
You may have alot of seal leakage in the front clutch circuit, could be the pump to drum rings, or even the front servo leakage (you did put the seal ring in the servo cover?)
If the shift is slow even in manual mode, then if the restrictor was used in the case, I would remove it, and the front clutchs should apply quicker.