Well, since the dealership technician cant duplicate your concern, the next logical step is to take one for a road test and demonstrate it for them if possible. I have been on many a road test with vehicle owners over the years and sometimes this is absolutely necessary. My thinking is that the truck is probably doing what it is supposed to be doing for the driving conditions you are subjecting it to.
With that said, you could do a little research on your own. If this concern happens and you are NOT BRAKING it is not likely an anti-lock activation event though a sensor signal dropping out could cause false ABS activation. Read on... I am thinking you are probably experiencing a Roll Stability Control (RSC) event or traction control activation. The traction control system with RSC aids in the prevention of excessive wheel spin, which allows the vehicle to maintain traction during acceleration especially on slippery or uneven road surfaces. This is accomplished by using the PCM to modulate engine torque and the ABS module to cycle the vehicle brakes. Both the PCM and ABS modules work to reduce drive wheel spin by momentarily reducing engine speed and applying vehicle brakes. You could turn off this feature (consult your Owner's Guide in the glove box) and drive in the same place where you know you can duplicate the concern and see if anything different happens.
You should also be aware that modifications to the vehicle such as larger tires than it was built with and suspension lift kits can adversely affect the proper operation of the RSC system. I am not making accusations, just putting that out here as we have no information about your truck in your signature and I wanted to make sure I covered that possibility as well.