High RPM and slow on the track. This usually happens when a track is hard, dry and fast. This happens frequently when there are more karts on the track than usual (State, National or $ race).
With plate classes, you may not even hit your desired RPM, especially with green plate.
Taking teeth off rear or adding tooth to front you will gain RPM and speed.
Here's some more:
Gear bound feels like the engine just stops "pulling" (accelerating might be more appropriate term to use) towards the end of the straights.
Look at your tach -- especially in lap replay mode. Look for tell-tale signs of the engine peaking too early on the straight on not continuing to increase in rpm before corner entry (as racing promoter suggested.)