Sounds like a fun trip!
My List of things to look at would be as follows:
AAA - Highest Tier.
Wheels/Tires:
- Bearings
- Inspect Shape of the spare
- Inspect Shape of all your tires
- Brakes all around
- Flush Brake Fluid
- New Brakes
- Inspect Brake Lines, maybe look at SS lines to mitigate heat going up I5 you will hit a lot of mountain passes.
Engine
- Not my strong suit with these, undergoing an LS swap now. My next G-Body will have a stock 3.2.
April...
AC
- Inspect AC, if you've got it.
- Recharge, even retrofit if you've got the time.
Comfort
- Do your homework on hotels in the areas you will want to hit.
- Closer to the date of the drive use a weather route app/site to foresee unfavorable conditions.
https://morecast.com/en/plan-your-route
- April is still tricky with some of the mountain passes unless you hit them mid-day.
Triple check all the fluids and have a bin for emergencies