Check Engine light question (Tranny Related??)

[mysvxrocks]

So my check engine light comes on when I start my car from a cold start, and its causing my tranny to not shift correctly. Ill floor it at like 20 and it seems like I am in 4th gear... the RPMs will go up correctly, but there is no power to the wheels. It will stay on for maybe 2-3 minutes on a cold start, then when it goes off, everything works correctly again, and the tranny shifts smooth. Anyone have any idea what it might be? I asked about checking it for codes, but the people at the auto store said it wouldn't show anything unless my CE light was on. Which it never is by the time I get to the store. Like I said, it only does this on a dead cold start, and does not come back on, even if I shut the car off and turn it back on again. Any ideas? Thanks -Dennis