Yes, I know the 3.0 v6 tends to seem gutless when in fine condition, but mine has trouble staying above 40mph, 2800-3000 rpm in 3rd while going up only moderate, at most, hills. Where should I start to get some more power back?

 

Tune up cap rotor wires plugs and shoot da timing

 

Check compression, tune up (as mentioned) using stock Denso parts & dealer air filter including cleaning throttle body (no solvent on or in tps - that'll kill it) and setting timing, check for codes, run a bottle of Red Line SI-1 Complete Fuel System Cleaner through the tank, replace fuel filter if not done in a long time, check for vac leaks in hose between air meter & throttle body, and elsewhere around intake and all vac hoses, replace O2 sensor if over 90K miles, lift truck and make sure no brakes are dragging, check fuel pressure, check resistance of both circuits of coil when hot (using hot specs), check ECT, TPS & VAFM per fsm specs, make sure throttle plate is horizontal when gas pedal is floored...

 

Check your timing. Stock is 10, but for more power you can advance it up to 15

 

All that has been said is good but what i did besides normal wear items is i built a custom cat back 2.5inch exhaust with a aero turbine muffler, put a weapon R intake on with a dry foam filter. After all that i had more power and 18mpg's in town and 24mpg's on the freeway.
Now i run lower gears, 4:10's, and 35's and i still have power to do 55mph up hills and get 20 to 22 on the freeway. '
The only other thing you can do is headers but they are super expensive unless you find them used

 

I also installed a 2.25" Borla cat-back in '96 and saw highway mileage go from 20 to 24 and there was a very noticeable boost in power (so the stock muffler must really suck). Before that I installed a K&N filtercharger intake, which despite its reputation for not filtering very well does allow the intake to breathe very well. I saw absolutely nothing from the intake except a bit more noise. No mileage change at all. Whether the Borla cat-back would have given as much benefit without first opening up the intake, IDK, but probably the intake makes little difference. With the ethanol swill coming from the pump these days, I'm lucky to get 19 on the highway, grr.

But, I think there must be something wrong with the OP's motor that should be addressed before messing with performance mods.