I own a 1999 Ford Explorer XLT with pretty much every bell and whistle available back then. I bought the car used and it now has just shy of 300K miles on it. Most of the driving is Highway miles and it is in almost perfect shape. I need to drive from Las Vegas to Sacramento (506+ miles each direction) twice a year and so far the old girl has gotten me there and back with no problems but with 300K miles, I get very nervous about driving long distances anymore. I try to keep the oil changed every 3K miles and keep it tuned up and ready but still those miles scare the crap out of me. I just turned 70 and have health problems or I would do the work myself. I have done similar rebuilds and swaps 20 years ago (and earlier) but that is beyond me now.

My question is:
1. Rebuild the original 302 and transmission
2. Buy a crate 302 and transmission and have them installed
3. How much will each option cost me? (roughly)
4. If I go the crate route what is the latest year (and highest reasonable horsepower (higher than the 215 HP stock or close to 300?? horsepower motor) I can have installed?
5. If I go with a crate transmission, are there better options for the AWD than the stock?

I know an Explorer is not a race car but I would love to give it more power than stock. The old engine still has get up and go but I hate to push it due to the mileage.