won't shift to 3rd at high rpm

[buthead]

First I will say thanks for any input. I drive a 2003 GP with a 3.1 (about 170,000k). Over the past year I have noticed that she has become slugis off the line and when getting out to past. I serviced her with new plugs, wires, air cleaner, fuel filter, and a trani flush. This did not cure the problem. Resently on the highway pulling a hill with my foot in it, it would not shift out of 2nd even after cresting the top. The check engine light came on but did not log any codes. Since then I can get it to do the same thing at will. Foot to the floor, trani down shifts to 2nd speed increases to 120km rpms @about 5000 but trani will not shift untill I let up on the throttle. If I hold it @ 120 / 5000 the check engine light comes on. I have done this with a Snap-0n reader plugged in and it doesn't log any codes, it does however show mis fire, mainly on cyl 1 & 6 more on the later. Any suggestions or comments would be great, and once again thanks.
Rob
aka Buthead

 

[buthead]

This one must have stumped everyone because there was not one reply. Well for anyone in the future that may have a similar problem, this is what I found. but before I tell you I will say that the techs at the local GM dealer had no clue what the problem was, it took a couple of bears after work with some coworks to find that all it was was a CAT starting to plug up. Easy fix, install a new CAT and she gos like a scared rabit. Hope this helps someone in the future.
Cheers
Buthead

 

[JimJimSpa]

My 94 Grand prix has been doing something like that too once i get up to about 55-60 mph if i get the rpms over i'd say 2200 it will rev up really high and won't shift and then when i get to the lower speeds it will stay in 2nd gear even when i manually shift it. I'm going to try that CAT thing and see if that works.
Thank you for the information!

http://www.grandprixforums.net/f71/94-grand-prix-shifting-problems-31630.html
here is the link to my thread if you want to check it out.