p1670 is a electronic feedback signal code from the idm to the pcm, everytime ive ever dealt with that code it ends up being a hassle and leads you know where , usually dont find anything , i dont think that its te reas you truck is cutting off at times , but if you want to test the circuitry for that code , there is a grey and white wire between the two modules , check the resistance of that wire , thats is the only wire on that circuit for that code