Whats the year and Engine size?
2.9l or 3.0l

For either you already have a Cold Air Intake(CAI) so no benefit in changing that.
You have factory headers set for mid-RPM power, so can change those for lower RPM power.

Switching to an electric cooling fan vs current mechanical fan will add more power for rear wheels AND make for better MPG, one of the only changes that does BOTH.

If you have a 3.0l then you need to drive it as it was designed to be driven, it is a HIGH RPM engine, it needs to be above 3,000 RPM to get any power, best power is at 3,500 RPM
Most engines make best power at 2,500 RPMs, and if you drive the 3.0l Vulcan engine that way it will be gutless

Outside of the electric fan conversion there are no inexpensive ways to get more power from a 3.0l, and unless you are racing in a 3.0l limited displacement division no reason to spend alot of money trying.

Morana Racing has some options: Tom Morana Racing Engines

Gasoline has a set amount of power per gallon, laws of physics
So there are two ways to add power
Lower the weight of the vehicle, power to weight ratio
Or increase the amount of gasoline burned per minute

Gasoline has a 14.7:1 air:fuel ratio, and this is a WEIGHT RATIO, 14.7 POUNDS of air to 1 POUND of gasoline, 14.7 grams of air to 1 gram of gasoline, this is why 200MPG carbs and "pre-vaporizers" are hooey.

So the more air an engine can pull in per minute the more gasoline it can use so the more power it can generate.
This is why a 5 LITER engine can generate more power than a 3 LITER engine, it can pull in 2 more LITERS of air every 2 RPMs, so it can burn more gasoline.

And why super or turbo chargers work to add power, they FORCE more air into the engine so more gasoline can be burned and more power generated.

So more AIR = more power
More gasoline without more AIR = FLOODED engine, lol

 

does anyone make an underdrive pulley for the 3.0?

 

I think they did but not anymore, might be able to find one on ebay.

Underdrive came from V8 hotroders and is a % improvement in horse power, you might use it when you got engine above 300HP with other upgrade, and then you would be looking at about 10HP.
On a V6 with 140HP it "might" get you 2HP, not nothing but you also need to add an "overdrive" pulley to alternator because it would no longer charge battery at idle, so cost becomes a factor.
Which is why they don't make them any more.

 

ahh - I added one to my 4 banger s10(a whole 119hp at the flywheel) and while it alone didnt help a whole lot (so yea 2-5hp is what to expect) it did seem to spool up quicker. It plus a header and efan did help free up some low end torque in that underpowered truck (96hp at the wheels stock where yes we have a local rather long steep hill and if im going 60 at the bottom i could stay in 5th gear and be 50 at the top, before id have to downshift to 4th as 5th started lugging) yes i ran a smaller alt pulley to keep up at idle.