Should I replace my TRUCK tires before Alaska trip?

I'd probably change 'em. That's a long drive, and probably some barren stretches, so last thing I'd want to worry about is my tires.
Tire Rack's advice is that if rain and wet roads are a concern, you should consider replacing your tires when they reach approximately 4/32" of remaining tread depth. 4/32" is an 1/8th inch, and you're at a 1/4" so, kinda close in my mind for a long trip.

I'd probably pack two spares for the TT.

Mike