Eightball

My alternator fuse(#4) kept blowing and it would kill my alternator, cruise control and speedometer. So I took my car to Honda and the sensor wires to my aftermarket downpipe had rubbed against the subframe and shorted out. They wouldn't cover it under warranty because the aftermarket downpipe. I get my car back and now the speedometer is really slow. It was working fine when I took it to Honda. When i take off it stays at 0 then slowly goes up. When I slow down it stays for a while then slowly goes down. Has anyone else had this problem? Will Honda fix it under warranty or blame it on me?