I have an 04 Grand Prix gt and this problem has gone on for awhile now. I've taken it to two mechanics, the first one saying I simply needed a transmission fluid replacement and the other saying he couldn't figure it out. To explain the problem further, this usually only happens from 3rd gear to 4th, or from 4th down to 3rd, but once the shift is made the RPMs will surge up and down and will continue to do so until I let off the gas a bit or push harder on the gas. The second mechanic replaced the mass air flow sensor and MAP sensor in an unrelated issue, but told me about the p1811 code being thrown, and I'm guessing that had something to do with my problem. Just looking for advice on what could possibly be wrong and what to do about it.
