just finished installing tb

I have seen many people report rpm issues after TB install. They say it goes away after a few days. You reset the PCM right?

If you continue to have slow dropping RPM you can always do the copper cap mod.

+1 for copper cap mod

Normal? Yes, reset the computer (if you haven't done so yet and give it a week, it will get much better (90%+), though it may never be exactly like stock again with the new TB. I ended up adding the copper cap mod as Kilgore suggested and it helps a little. Actually I did this over a year after adding the Accufab TB and plenum just to see what all the buzz was about.
Here, see my attached pic. See the little black 'box' in the foreground? Disconnect the hoses from the left and right sides of this box (Actually I disconnected the hose from the left, but kept the hose on the right side of the box, disconnecting the hose from the plenum). On the left side is where you will make the mod. Take this 'box' to your local hardware store and find a copper pipe plug or fitting that fits in the left fitting snuggly while still allowing the hose to fit around it. Then (buy it of course!) and drill a 1/4" hole in the center. Fit it back into the box then put it back together on your car. What the cap does is limit the amount of air the engine gets during its return to idle, thereby making the RPMs fall more quickly.
Best of Luck!