i think your mp-8 has issues or its the wrong one for you/

 

He pm's me and got it fixed. He said it ended up being a loose wire on the MP8's wiring harness.

 

I would go back thru and unhook the battery terminals and then unhook the mp8 and go from there. if it ran fine before something is not right with the mp8 I would say. I dont know what the rail gauge would have to do with the truck running badly. I installed the rail gauge on mine it had a ground wire, some leads to the fuse box and a plug in for the rail. dont know how you could mess those up. I would call ts performance or someone at a shop to help you out, that way you dont damage your truck.