FWIW I used Severe Gear (the blue stuff) in a 1999 Jeep Cherokee after about 30,000 miles, didn't change it for 20 years and it still looked good when I would check it. The car was a spare we had setting around for my wife who worked at a hospital and had to get to work for her shift regardless...
Those 3.9 Dakotas seem to last longer than any other truck I know of, though. I've seen two with over 400K miles and one was on the original transmission. Both never had the motor opened up for anything.
I did a road trip to FL a couple of years ago along with some around town driving and I averaged a little over 18 mpg in my 2012 Chevy fullsize V-6 cast iron 4.3 with the 4 speed auto transmission. It's not as good as the usual 20 mpg but I-95 moves fast. The truck is 2WD and extended cab.
I've found from experience that universal joints without grease fittings last longer than the ones that have them, but ball joints, tie rod ends, etc. that don't have fittings don't.
I've owned two Challengers; a V-6 and a V-8. Honestly, my favorite one was the six because of the smoother riding suspension and automatic transmission. My R/T had the manual transmission and the ratios are screwy on that transmission. My suggestion is a SXT Plus (gives you leather seats...
If you can find an older Toro Super Recycler it will basically last forever. I scavenged one from the landfill about 4-5 years ago and decided to fix it up with a new Briggs motor, drive wheels and a few other cables and parts that were getting worn out. I put a total of $360 into it but it gave...
FWIW I had a 2008 Colorado and traded it for a fullsize Chevy (2012 Silverado in my profile). The full size is much more capable and didn't really cost much more than a small truck. Reliability has been almost perfect. I had a fuel tank pressure sensor go bad and replaced it for $30+ with a...
If the transmission goes out, it can be fixed when it actually goes bad; it's a separate component. What he knows now is that the motor seems to me like it's worn out and since this vehicle is used for making money downtime is a major consideration. It's admittedly a difficult decision, though.
I thought the motor should be replaced with 200K miles of local delivery service. If they planned on keeping it, may not be a bad idea to do an oil pressure and compression test, maybe leakdown too. I'm a fan of his channel.