Some new info.... I stopped at the dealer and explained the situation. After some digging we found that the truck only has a 3.73 rear gear. I asked this when purchasing and was told 4.10. Should've checked the build sheet personally and not trusted the salesman.
This may explain some sluggishness pulling but does not justify what I experienced. They are going to scan for codes (no dash lights occured)and reflash the computer next week. I won't have a chance to tow any steep hills again this summer though.
To clarify the occurance, each time the hill was started from a stopped position, always seemed to be red traffic light at the bottom of hills. If I was at speed when starting other hills it would pull ok. Lose a little speed but it would downshift with throttle and hold or accelerate.
To answer others, I use premium grade fuel when towing and the air filter is clean. Wondering about the fuel filter though. I have noticed some hesitation under harder acceleration (non towing). Acceleration isn't smooth and linear feeling, it surges in power.
The Tundra had a drop-in k&n filter but no engine mods. It had a 3-1 suspension lift, air bags and 305/55r20 E rated A/T tires.