Lake Austin is pretty chilly also. It's fed from the bottom of another lake. They are all man made aorund here. The water temp on the north side of the lake is around 67deg. That's really chilly, but refreshing when it's 100 outside.
Lake Shasta sounds like a great place.
No more trucks, but this is what I used to have. 2000 GMC Sierra, 6.0L-LQ4, Built 4L60, LS6 Cam, The Other Guys Headers, 3 inch exhaust and 7 chamber flowmaster, 43lb injectors, Nelson Tuning, Drop - 3/4 McGaughys Spindles, Bell Tech Shackles & Hangers. Best time 13.59 @ 106