Original post by: MOtech9 ,
sounds to me like either it may have the wrong lube in it or most likely the specs on the sliding clutches in the tranny are out, either from wear or not being right from the start and then causing them to get out further quickly, Does the truck have the Tranny cooler installed and free of air flow blockage? if so may think about replacing it, many times they are just set aside and reinstalled after a reman without much being done to them. could also be that something wasnt shimmed correctly causing the teeth to not mesh correctly and as the load/torque increases it puts more or less gap in them and then you have the chatter. without removing the unit and having it opened up and checked out pretty much everything is speculation, on another note I have seen plenty of differential noises and vibration travel right up to the shifter and into the cab causing a misdiagnosis, my advice would be to start looking for a GOOD gear shop and have them ride along while it is making the noise.