My experience after buying a lifelong contractor truck at 170k and have driven it 60k miles since, '99 5 speed 4x4 with 4.10 gears:
I got it sometime after the clutch and 5 speed had been rebuilt, and someone had done reman heads (have no idea the mileage on the truck when this work was done). I installed a permalock in place of the vacuum actuator as I don't but tons of miles on and mileage doesn't really bother me. Since then, I get about 10-12mpg unloaded, worst of 6mpg towing 18k. I put a TPS in it not too long after I got it, that cured an intermittent miss/hesitation, had to put a carrier bearing in the driveshaft before I drove it back from AZ. I have done nothing but tuneup and oil changes since I got it until I had the timing chain go about 5k miles ago. I cleaned up the timing cover/oil pump housing and installed a new oil pump gear. Oh, and I replaced the fuel pump/sender/filter assembly about 195k, it was the factory unit.
Known V10 problems:
They used a stupid Fram PH16/Wix 51085 sized filter from the factory (those are the actual aftermarket replacement part numbers BTW). Fuck that filter. Install a Fram PH8A or a Wix 51515 size filter on it. Factory filter goes into bypass quickly (system capacity is 8qts. so it's got a lot of oil to filter). Lack of doing so and not changing the oil every 3k (or less miles) leads to issue #2.
Timing cover/oil pump housing is NLA. Oil filter going into bypass leads to scoring of cover and pump gears. MIne had both, I just flap-wheeled the housing to smooth it out. Clearance was out of spec, but with 10w-30 it carries 35-40psi hot and 60+ going down the road now. I would like to pick up a used one sometime and machine out the housing for a brass sleeve to fix it permanently.
98/99 model years supposedly had some head porosity issues, perhaps that's why mine were replaced. If it's not having issues here 25 years later, I'd say you aren't going to have that issue or it's already been addressed.
94/95's I'd avoid, as there are differenced in sensors and front timing cover that make them a bit different and harder to find parts for.
That's it. Can't find another fault with it.
I don't know why anyone wouldn't change the back plugs, I didn't think they were bad with a Snap-on spark plug socket with the built-in U-joint and a 10" extension. Keep the engine tuned up (plugs/wires/oil/filters). Fuel filter is on top of the sending unit, gets replaced when replacing the assembly. You can replace it separately but I'd just replace the whole works if you need to install a filter. I have had no injector issues, and dropping the tank, replacing the pump assembly, and reinstalling was about a 2 hr. job (AZ truck, but has the 35gal factory tank that was 7/8 full). Spray penetrant on the hardware the day before you do it and you'll be fine unless it's a 100% rust belt truck. I change the oil with a Wix 51515XP filter and full synthetic oil about every 4-5k miles, oil typically looks to be in good shape when I do. If running conventional, I'd religiously do it every 3k or less. There is an even larger capacity filter (Wix 51715? not sure, it's taller) you could use, but I don't because I do use it off-road some and the filter would hang below the crossmember. The 51515 still stays above it so I feel it won't contact anything if I have to go through a creek crossing in the middle of a field somewhere.
If I unlock the front axle or drop the driveshaft, I can get 14mpg at 70mph average. Got 14.5mpg driving it back from AZ (Front actuator not working and disengaged) on interstate stretches running no ethanol fuel the whole way. Running no ethanol seems to improve the MPG about .5 for my typical mostly towing, mixed driving so I don't think its worth the extra $ unless you are putting many miles on it.
If cold starting is ever a concern, I've had it be the only gas vehicle start on a -30F morning with wind chills about -40F.
With the auto I wouldn't expect those mileage numbers, but I bet 10 is doable for unloaded driving easy, especially when most of the autos I've seen were 3.55 gears. I wouldn't be afraid of it, but I wouldn't make it your daily unless you were going 20mi. round trip.
