From what I've seen there seems to be an error in the NTSC-U version of this game that prevents the ghost from working and stops you from recording your times. The PAL version fixes this, but runs at 50fps and also removes all of your afterburner each lap in time trial mode.

Also, regarding checkpoints, the game lets you skip one checkpoint before disqualifying you, but if the second checkpoint you skip is the finish line the game still seems to record your time. I did this accidentally in my Husavik Race Way run but I'm not sure if it should be allowed. You could save a lot of time in each track this way, it's something for future runners to discuss.