I don't mean to sound like an old fart, but can I ask why you want your engine to rev high? Besides lack of lubrication (or in extreme cases, insufficient cooling capacity), excessive rotational speed is the quickest way to destroy a reciprocating engine.
The centrifugal forces developed by operating an engine above design speed are enormous and those loads are carried by the crankshaft, rods and bearings.
Okay, I'm done with preaching so a few questions:
What is your road speed with the engine at WOT and the transmission in 4th gear?
If the transmission is put in neutral and the engine is revved, can you exceed that 3K limit?
What is the ratio of your gears in the rear end?
Do you have oversized tires mounted?
Have you checked to be sure your throttle plates can open fully (and there is plenty of fuel flow, no exhaust restrictions or lack or combustion air)?
Maximum engine RPM is a function of external load. If the throttle plates can go wide open, plenty of fuel is available and there are no exhaust/intake restrictions - that's about all you can do (provided everything else is in good order).
When the accelerator is pushed to the floor engine speed will increase to a point where it's available horsepower limit is reached.
If the transmission is in neutral, there is essentially zero load. Go WOT in neutral and I assure you, you'll get more than 3000 RPM - course you will also quickly destroy the motor.
Start driving and apply an external load. Now you'll notice that the rpm's will not increase so quickly. Shift to a higher gear and go faster. Wind and rolling resistance will steadily increase the load on the engine. At some point you will reach the engine's design power output.
To answer your question; you might have a set of gears in the rear end that have a really high input/output ratio. You might have huge tires. They cover a longer distance in one revolution than a stock tire. Either of these two variables will tend to decrease engine rpm for a given road speed.
The idiots that rev the **** out of their motors, light em' up - and brag about RPM, are getting no more power from their plants than you are. They just blow their load quicker.
You might take a while to catch up. But when you do, your engine will be breathing easy - just cruising along. Those guys with lower gear ratios and smaller tires will need to crank the **** out of their plants just to keep up.
The reduced stress on the engine internals due to lower RPM's will greatly extend it's life - that's the payoff.
And remember, these trucks were built for work - not play.
