WHAT ENGINE? If this is a V6, you're screwed. If this is a 305, you're almost as screwed. If this is a Diesel, you're screwed. Sell the truck, get something that has more power to start with.
FIRST, you need to assure that you have all the power you're supposed to.
There is no point to buying expensive "hot rod" parts to make "two hundred more horsepower", if you've got bad compression in three cylinders. Fix the bad compression, maybe you don't need the expensive aftermarket parts.
OTOH, if you have bad compression in three cylinders because the valves are burnt, maybe you want to buy the expensive aftermarket aluminum heads--which will fix the bad compression AND give you additional power.
The trick is to verify that nothing is "wrong" with the engine; or to
know what is wrong.
Start from scratch:
Cranking compression test. If any cylinder(s) are bad, you want a
cylinder leakdown test of AT LEAST the bad ones, and the best one, for comparison. Find out where the pressure is going--out the intake valve, out the exhaust valve, out the head gasket to the cylinders next-door, or into the cooling system due to a cracked casting or failed head gasket.
Verify fuel pressure, at idle, and under load. How old is the fuel pump? How old is the fuel filter?
Ignition coil output test. Spark-testers are about $15 on Amazon. Get one calibrated for HEI, not "points" or Chrysler electronic ignition.
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Connect a scan tool, look at ALL the sensor data--coolant temp, TPS, O2 crosscounts and voltage, MAP, vehicle speed, Knock sensor, and all the rest. Then verify the computer outputs--IAC, spark advance, EGR, etc. Check for "codes" but the sensor data is usually more helpful.
When was the last time the thing got a
thorough tune-up? Distributor cap, rotor, plug wires, plugs, fuel and air filters, verify the thermal door in the air cleaner snorkel. Make sure the EGR and PCV works right.
How old is the O2 sensor? Anything over 50K miles/5 years is suspect.
Catalyst plugged? Exhaust restricted for some other reason?
Failed distributors (cracked magnet at the pickup coil) are pretty common on TBI engines. Leads to misfire and stalling. Misfire reduces power.
Make sure the throttle opens all the way by having someone you trust push the gas pedal to the floor. Bent lever arm at the gas pedal may cause the throttle to only open part-way, for example.
Do the brakes drag? Does the trans slip? Do you have bigass tires and 3.42 gears? Maybe the engine is not the problem--something else is sucking power.
SECOND, "400+ torque and hp"
might be realistic, if you have a 7.4L. "400+ torque and hp" with a TBI 350 will be VERY expensive, and you'll throw away or massively re-tune the OEM computer. "400+ torque and hp" with a 305 is wishful thinking.
