I have access to making TB Spacers and Plenum Spacers for 3.0 V6 engines. These offer a gain in power, I noticed a good mid range bump.
Here's the TB spacer

I also have more Mod knowledge to make the 3.0 perform better.

 

Making and adding plenum spacers makes a good mid-range improvement. (I have the ability to make them).

If you have the stock airbox drop it in favor of a cone-filter/ short-ram style.

If you have the 46mm throttle body swap it for a 52mm found on 3.3/3.8 vans.

The ignition timing can be advanced to roughly 15*. (I'm at 18 on mine, but have supporting mods).

If you are capable, pull the plenum, split it open, port/polish it.

Depending on how much you want to tear apart, swapping the stock cams for 92-96 Mitsubishi Diamante SOHC heads nets a gain from mid range up.

I have all this and more done to my 3.0. It went from a low-end motor to a great all-around motor. Biggest issue with the 3.0 is they don't flow well in factory trim, if you fix that the 3.0 really comes alive.

 

Almost two-ton minivan with a engine that has around 160HP and 120ftlb torque.. Just a few of the mods listed will easily knock a third of the fuel economy off and drastically increase powertrain wear.

If I WAS going to do it I'd do it with a local driving 3.8l Caravan(no Grand). More stock power and minimum weight. The best sensible mod I've seen to date was aftermarket dedicated tranny coolers.

 

141hp 171tq.

3.8's are only nominally more then that at 162hp 191tq, which a 3.0 can easily overcome, and have better economy while doing it. My 3.0 used to be hard pressed to pull 24mpg, now I rarely get under 28, and have plenty of power when needed.

Like I said the 3.0's problem was flow, improve the flow and they improve all the way around. They not like a lot of other motors.

The A670 trans was junk w/ or w/o trans cooler. But that issue can easily be fixed in favor of an A543 manual swap. That's about the only driveline issue, and that's bound to be an issue regardless.

 

Later 3.0's were 150hp 181tq.

 

The cam and timing options can't not increase consumption and material decay.

I only deal with 3rd and 4th gen and usually go for the 41TE even though they were garbage on 3rd gen(because of valve bodies and TCM firmware). Because they get better MPG than the other autos. I use aftermarket coolers and keep factory engineering because mine are used for travel and pulling 1/2 ton stuff. The fuel economy and wear in my conditions reveal bad tuning decisions very quick..

I've drove both 3rd gen and 4th gens from ocean to ocean with 1,400lb campers attached. I have slotted&drilled discs on mine with large silver&aluminum based coolers for the trans. I DO use those turbine shaped fins in the air duct but haven't noticed a difference..

 

The timing possibly does, but you also have to remember, the 3.0 runs 12* advance stock, and the timing advance is mostly to make use of the supporting mods, at which point it helps.

The 41te is mostly junk because of the solenoid packs on the earlier ones. This can be solved by adopting the later year solenoid pack to the older trans. Dodge got it right on the later 41te (A604), well ok at least better.

You won't notice a difference with the fins in the air duct. They don't allow any more airflow and adding swirl to the air that far from the ports just slows it down.

 

I will say towing where you're under load, you'll have more power to do it, but will most likely hurt your mileage.

Cruising down the highway, it will help.

 

Correct me if I'm wrong, but isn't the 3.0 completely different from the 3.3 and 3.8L as it's a totally Mitsubishi design?

 

Different engines and designs yes, but some parts interchange. Throttle body is one of those parts.

3.0's ran a tiny 46mm tb, whereas the 3.3 and 3.8 ran 52mm's.