TB Questions

I recently switched my stock 03 atx tb to a damnit pnp mtx tb. I know that the spring is softer, however i didn’t think that it would make a difference in my idle. With the new tb when i start my car it revs up to 3k then drops to 2k and very slowly goes down to just under 1k. If i’m sitting still in park and rev it up to 2k it will stay there longer than it should and will not go right back down to idle like it is supposed to. Any suggestions?? I have also noticed that since installing it my car when in gear without touching the gas will cruise along at 10-15mph, when before with the stock tb it barely moved especially with my heavy 17" wheels on. I also have some questions about my transmission. When i put it into reverse it clunks rather loud and shakes the whole car. I checked all fluid levels and everything is ok, dunno what to do…

mine did that for a while but then the computer reset everything and now it’s back to normal–but it did take a while