I own a 2001 f150 with a 4.2 and a 5 speed manual transmission. It currently has 260k miles on it and I just noticed that it won't rev above 3500 rpm. It feels as if its starving for gas or has a rev limiter. I am not sure when this problem occured because I normaly never rev the motor over 3000. It will rev up normally when in neutral but when i am driving under load it seems to drop when I hit 3.5k. Anyone have any idea why this might occure. Ive changed the timing chain and sparkplugs and sparkplug wires in the past few years, but thats about all ai have done on the motor. But I have no idea when the problem began to occur. Not the biggest problem in the world but just find it annoying that it won't go over, makes me feel as if something is wrong with the truck

 

Something is definitely wrong. I would first inspect the intake air tract to make sure the filter is not clogged, the mass airflow sensor is clean and there is no obstruction in the air way - look at the throttle body too. Then I would inspect the exhaust system to see if there is a crushed pipe or other obvious obstruction. You probably should get the cat converter checked because it could be clogged. At the same time you might go to the auto parts store and see if there are any codes saved.
You changed plugs at some point - maybe you should revisit them to see if a couple have worked loose or the boot is arcing. It could be a clogged fuel filter too - there really are a lot of inexpensive possibilities (not counting the cat converters, of course).

 

Ok my can go over 6000