Sorry about your loss Dan but we move on with the loved ones in our hearts and memories. I recently lost a younger brother who took his own life battling booze addiction. Mom lost him and a sister and brother in a week real hard on that old woman but she moved on.
Now on your truck your worst than me. I would say get frame and engine sorted out first than paint and upholstery last. I know you have the truck at painters but are you not afraid it will get scratched when put on the frame? Well I am little different both mine haven't left the premises and I rather do stuff a little at a time now that I am retired.
The 5.3 motor is a good choice, the 6.0 does eat a little more fuel when punch computer or not. The guys say oh I get 22 mpg, yeah on a cool day with the wind behind your back. The choice on LS motor is good and tranny can't beat, now you will need a new rear end with 3.73 gears to go with over drive tranny. More changes what a nightmare well you will be happy once it done but don't get to crazy a daily driver gets beat up more than a trailer queen.
