ecm

hello all just had a problem with a 06 c15 acert ecm i changed the batterys and then all it would do is tune over i was told that the battery in ecm was bad come to find out ecm and battery was no good.......now i went and got a nother one of a 06 kw t2000 same c15 acert started right up but speedo rpm oil water none of them work my guy that dose the work said it just all had to be changed in side the ecm.. is he right? ok i had a kr scane gauge hooked up so i could whatch the oil and water now it dont read.. what the heck it all went out in waco tx on way home to south ga evey one says just ride with it that it will be ok till i get home and get it all set.. what do yall think are they telling me right..? thanks will