First check to see you have good, solid connections to your transformer and track, and you are using a good, heavy gauge wire.

Next, check to see all the pins in the ends of the tracks are clean and rust-free, and are tight fitting in the ends of the tracks. Squeeze the track slightly if necessary to get a tight fit.

Lastly, make sure your track is clean and free of rust and dirt, including the ends where the pins push in. Use a ScotchBrite pad to clean them up, followed by a wipe down with a rag dipped in Naphtha.

After all this is done, you should get consistent voltage readings all around the layout. A lighted car rolled around the track will also confirm consistent voltage.

Larry