I’m never quite sure how to view the 4L60. If the OP is not exceeding the rating given by the OEM for his truck, then this trans should take it, and its not abuse, right? assuming all the details are considered, GCWR and all. But then at this age any failure is hard to tell apart from normal wear and tear, right?
Half tons aren’t “meant” to do this work day in and day out, like a 3/4 ton. Yet OP is not doing this day in and out, just a few trips a year, so… its still light duty usage.
Although 6k trailer plus the usual stuff in the vehicle does strike me as at or beyond the limit of a half ton. Let alone any future upgrades to the trailer.