Driving down the highway at about 2000 rpm truck started running really rough, it couldn’t maintain speed. Pulled over, the truck idled fine. Started trying to drive again and it would start breaking up. Once parked I slowly increased rpm at about 1800 it would start to run rough again. If I went above that it seamed to smooth out. Started driving again I noticed this rough running would occur between say 1200 and 2000 rpm. At some point it smoothed out and began running fine again. Two days later the same thing occurred, it began running fine again later in the day. No codes at anytime. Engine was replaced about a month ago, crank sensor and plugs were replaced at that time.

 

maybe 02 sensor. maybe fuel pump/fuel pressure. maybe clogged cat preventing high rpm rev.