I have had the experience owning both a gen 1 and a gen 2 Tundra. My boat is around 6500 and 7000# so I am in a similar situation to you. I will tell you that with that weight the gen 1 can do it, but your will definitely feel it and you will be pushing things a little. The longest tow I did with my gen 1 was about 80 miles and the truck did fine, but it was working.
My 2007 pulls the boat like nothing. The truck is just built for heavier loads and it feels so much more comfortable. The 5.7 pulls like a champ.
In my opinion I would go for more truck than a gen 1 to pull your load. If you had a smaller boat, I would consider the gen 1.
_________________________
Tom
2005 FW Horizon 230
2007 Toyota Tundra Crewmax