I used to have the same problem on my 01 v6. I found that the MAF sensor gets dirty and causes this issue, especially due to oil coming off my K/N filter. Here is what i have to do once a year to keep it under control.
1. disconnect your negative battery terminal.
2. buy a can of electronics cleaner, take the MAF out of the car, and spray the MAF sensor heavily to make sure you get it thoroughly clean.
3. let everything sit for a while to make sure the ECU resets, and that the MAF dries out.
4. reconnect everything and your cars rpm should no longer hang up between shifts.