Agreed, the pressure treated material needs to weather-in for a few months before any additional treatment is applied.
Personally, I think anything Thompsons makes is really a waste of money. It won't make the wood last longer, that's for sure. You never see pros using it (or similar products like Behr) for good reason.
My advice would be to go with an oil-based penetrating stain/sealer. Penofin is a high quality product that will actually give you something worth paying for. Their 99% UV resistant stuff in the red can is about $40/gallon, and worth every penny in my experience. It'll help reduce the cracking, surface drying and checking that treated southern yellow pine is known to suffer. It comes in about a dozen shades including clear.