Having Some Issues

[RiotRUSH]

Good afternoon everyone. I have turned to the forums for help to figure out what is wrong with my 2003 Yamaha Vstar 650. I just dumped 940$ into her fixing a lot of issues already but the bike shop refused to work on her anymore. I guess I have a custom exhaust on her without baffles. This is creating a problem with the back presser issue. Now I bought this bike back in 2016 (Nov) and its been in the shop since then. I bought the bike for 200$ which I thought was an amazing deal then I slowly started to realize that I was sadly wrong. I can't go any faster than 45mph (60mph Downhill LOL) What do i do first? Trying to fix it myself now. Thank you everyone