My colorado has a very rough start-up. dealer saying that its normal…Like its starting in gear…very rough
Make him prove it. Have him get an '18 truck with the same engine and transmission out of stock and prove to you that they are the same.
If they are, the same, sorry, it was a bad choice of vehicle, learn to live with it.
If they aren’t the same, the dealer is obligated by GM to fix it.
@Mustangman has the right thing for you to do.
It should be easy for you and the dealer to walk out to any other 2018 Colorado with the same engine so you can see if it starts the same.