i currently got my car a diagnostic test and it said i have a huge vacum leak

It's common for the intake manifold to leak, but it's also possible the MAF sensor is bad and the computer assumes a very lean running condition. There's not enough info to go on to know for sure. I suggest you take it to a Volvo tech, they will be quite familiar with the issues you are experiencing. Also, the speedometer issue may be a bad ignition switch or ABS computer, again, have a shop look at this.