im having check engine light/ tranny problems, any hlp?

[tteal07]

hey i just recienly bought a 2005 dodge diesel it has intake exhaust and banks sis gun tuner. well my check engine light is on and im gtting alot of coded. i dont have neer the power that i should> every tranny place i talk to they say its in safe mode or whatever somthing like that. feels like im starting in second! dont have the power i should at all. and when they try to scan my truck it just says not connected. ahh just really fustrated. any help wold be greatly appricated. thanks