help : no third gear?

I have a 99 gmc sierra 4x4 5.7 with 460L tranny. I changed the tranny fluid and filter( what a job getting the pan off ) now with the test drive first and second work fine, but when it goes to shift to third it shifts but nothing there. Then I'll slow down and it will downshift to second ok.What have I screwed up? The transmission alaways worked fine before I changed the filter. I also had to disconnect the shifter, next to the pan but it sure seemed to go backk togeather correctly. Thanks for the help.

man thats not good.
take the pan back off and make darn sure you didnt pull a connector off the shift cylinoides

yep check out the solenoids make sure you didnt unplug one or bust one you can ohm them if you want the 2 shift sol. 20-25 ohms (the 2 next to each other next to the crossmember) the 2 up front are 20-25 ohms (grey connector) 10-15 ohms (blue connector).