You have only had the Truck for six years what proof do you have it's the Original Never Rebuilt Trans.. Mine was purchased Brand New by my GF with every Service Repair Record which is about 1/2''thick stack of Dealer receipts. I find it hard to believe myself that her (mine for the last ten years) trans made it 19 years and just shy of 295k. A person is lucky if these Light Duty 4L60's go 150k let alone over 200k let alone over 300k.
I bought it from someone I knew(original owner) and have all the service records. He even kept the window sticker with the records. He babied it and took excellent care of it. Most of the time his wife and daughter drove it. I do think the regular interval trans service I've done since buying it 6 years ago has extended the life to where I'm at now. The trans service I've done is just drain and refill from the trans pan drain plug every 50k or so, with one service around 200k of dropping the pan and replacing the filter. YMMV