idle won't level out change parts still 1800rpms in park and drive gear on 1998 Chevrolet 2500 Pickup

I changed the Maf, Map, Tbs, Iac, and idle starts out correct then rises from 900 to 1800 rpms. How can i fix it?

Asked by for the 1998 Chevrolet 2500 Pickup
I would be looking for a vacuum leak or air intake leak, providing more air than expected to the intake. You could have intake manifold gaskets leaking...