Wierd 4T60E Trans Shift Prob 97 Bonne

My 97 Pont Bonne with a 4T60E has started to slip between 1-2, 2-3, and
3-2 shifts. The engine will rev for a moment durring shifting and then it will catch itself. It also is upshifting a little to quick 3rd gear at about 22 mph, 4th gear at about 32mph.

The wierd part is it only happens when the gear shift valve is in D4(overdrive); if I put the gear shift valve in D3; nothing slips and it shifts perfectly(except it stops at 3rd gear as designed). I have a temporary work around; I start accelerating from a stop in D3 and then when I get to 50MPH shift to D4 and it goes in to overdrive fine.

I have:

1. Installed a new vacuum modulator
2. Tested for proper vacuum
3. Tested speed sensor
4. Changed fluid and filter.
5. Cleaned all electrical connections
6. Checked computer codes (none)

When I changed the fluid, it was clear/red with no smell, and the pan had hardly any clutch dust. Looked great!

I am stumped, what do you guys think?

Thanks in Advance,

-Pete

I would suggest a full scan with a trans specific scanner to look at slippage and gear errors as well as solenoid functions. The tps may be skewed also, but less likely.