guts meter is how close it is to being fully trained. and I have no clue what a gut shot is but I think it means when you tap a lot on a punching bag and your Pokemon will do a ultimate shot and break the training bag + random messages such as "Can Pokemon even move like this" will pop up.
Source: A Pokemon EVtrainer's Knowledge.
Oh! and I can give you a tutorial of super training but you can choose :)