I've been trying to tweak my wife's EXT for a while now, hoping to get a few more MPG out of it (about 15 MPG, now), but what's starting to happen is a "hunting" while cruising...

This happens around 60-65 in 4th, in a light cruise. The RPM's vary by about 300 rpm, bouncing up and down. I can't seem to find it while logging - the logging software doesn't seem to pick up the RPM changes that well. It also notes that the trans is in fourth, with the TCC locked.

Now I thought that if the TCC remains locked, that the engine RPM wouldn't change much relative to the vehicle speed (isn't it the point of having a locked torque converter?) - but I'm wondering if there's a feedback loop I've caused somewhere.

Any ideas or tune files you guys can put up is appreciated.

Thanks!