ant7188,
I'm ressurecting this one...
So what wound up happening with your tranny? Is it just shifting at a higher RMP point, or is it a true slippage, where the RMPs will shoot up and then the tranny will bang into gear?
The slippage wouldn't likely go away after the car has been driven a while. Does this happen only when it's cold out, or during warmer weather as well? I know the the ECU (Electonic Control Unit) has programming to elevate the shift points in cold ambient temperatures in order to bring the car up to operating temp faster. This is factory programmed. You exprience of it shifting fine after reaching operating temp leads me to think that this is the case.
Although it probably doesn't hurt to change the fluid and filter, just as means of checking the quality of the fluid since the rebuild. Depending on how many components they replaced with new ones, the tranny could have gone through a new break-in period and you may have abrasive particles in the fluid. New fresh fluid never hurts, you'll extend the life of your tranny as well. Just make sure it is refilled to the correct level. A second and/or third fluid / filter replacement shortly after the first one, is just has important as the initial one, in case the detergents in the new fluid clean some of the deposits or sludge. That's the best way to keep everything running as smooth as possible.
At the same time, make sure that the cooling lines, and/or the cooler don't have any restrictions or blockages, altering the fluid pressure, that will sure cause erratic shifting as well. Good luck, keep us updated...