I made my first solo trip cross country with nothing but my '94 Silverado (and a dirt bike)!
1994 C1500
5.7L 350ci (TBI)
4L60E
Before I left, I installed a transmission cooler and replaced brake lines along with general maintenance. The trans cooler helped so much - especially on steep...
4L60Es typically burn out due to a combination of design flaws and typical wear/tear rather than the amount of power running through it. Due to the design, the wear pattern on the friction band/plate is a common cause of failure. (A good rebuild kit can replace those flawed components)
The 4L60E should have no problem handling the upgrades. I would definitely put that money into the 350. It will give you plenty of power...Good luck with the upgrades!