Did you change rear gears?
Many people run into this problem when going to a higher rear gear ratio. I suppose it could happen with more power as well...
It's all about clutch fill time vs how fast your rpm is climbing.
IIRC there are a couple options to remedy.
1. Command the shift at a lower rpm so the clutch has more time to fill...
2. Enlarge a hole in the valve body separator plate to allow the intermediate clutch to fill more quickly.
Keep in mind, the 1-2 factory aluminum accumulator is known to wear out quickly on early transmissions, if yours is a 2003, it may have the bonded rubber already. If you're pulling the pan, it can be checked and or replaced with a bonded rubber replacement without dropping anything else.
I found the TCCoa forums (Thunderbird car club) has a wealth of information on AODE/4R70w mechanical function, issues, troubleshooting, rebuilding, and modifying.
https://www.tccoa.com/forums/automatic- ... sions.990/