ok...
the last time i dealt with an engine that did what you are describing and was not coding out i had to replace the throttle body.

Even when i ran diagnozer on it the accelerator sensor was reading good and had full movement detection from 0 to 100%.

And even the throttle body sensor was reading as ok but when viewed in diagnozer it showed it not moving to 100% every time.

this is the only thing i can think of at this time that might cause this problem.
The fact that it is not coding a DTC code for either the accelerator pot or the throttle body sensors is really strange.

just thought of something, since you replaced all those parts did you do the 'pedal dance' and clear out any old codes that might be in the history? try doing that and see if it helps

some of these K25 units have suffered this fault when the accel pedal is mal adjusted its like a pot on the old Raymond and can go over center so to speak
there are two bolts in the mechanism that need to be adjusted out just a touch this is assuming new vaporizer was correct and the fuel pressure is correct believe me I chased this one for a couple hours myself

no diagnozer is not available to the aftermarket crowd
it is a dealer/mfg diagnostic program and only on a very few certain special occasions where customers purchased large fleets on a lease program and had inhouse mechanics have i ever seen it used outside of the dealership program.

now that we got a serial number let me check a few things and i'll get back to you.

Brain fart! Model P6000, Serial AT13F02732
Engine info K25L, Jan.2006.
Thanks for the help! Do you know if the Diagnozer is available to the aftermarket.

the program used to diagnose the cat system is called "diagnozer".
on 2004-2006 models the screen is located underneath a dummy plate on the top of the injector holder body just over the fuel pressure sensor.
on 2007-2009 models the screen he speaks of is located inside the housing where the inlet tube is bolted to the injector holder body. It will be seated down inside with a small clip holding it in place.
K21/25 Tier 2 2004-2006 Injector Filter Part # 9042508330
K21/25 Tier 3 2007-2009 Injector Filter Part # 9196507800

how does the engine start? does it surge or backfire any while running? When you turn the key on , off, and back on can you hear the throttle body calibrate itself? If you replaced the vaporizer have you checked the fuel pressure and made sure it was set correctly? This system operated at 24 to 28 kpa fuel pressure so be sure it is set to that.

The fact that it will rev up the engine to full rpm's though leads me to believe that the fuel system may be ok. It sounds like your having a problem in the throttle body or accelerator. But the fact that it is not coding out is confusing. Generally when these trucks have any type of fuel system problem or accelerator or throttle problem they do code a DTC code.

One other problem i can think of is if this truck has the engine speed sensor reluctor wheel on the crank pulley with the mounted sensor i have seen this problem happen if that harness connecting to that sensor is damaged, the engine tends to not want to rev up correctly. You might want to check and see if this is on this truck.

Without a serial number i'm just throwing out educated guesses though ;o)

Thanks for the reply Robster. I do not have access to uptime software but this info will give me a good direction to go. There are no error codes showing for now. Is the filter you mentioned in the lock off assembly? I have replaced that one.

if I mind right the pcv system is linked to this hose to gas unit so that may be worth a check. I remember if you remove the rocker cap when engine idles then it runs crap due to this

still sounds like an airflow fault I have had on many Mitsubishi fg25n.
if I recall the error code is e21 but does not always show. check the wiring at air flow sensor plug back over engine to ecm in the left chassis, if its an older truck this wiring can get brittle with heat/vibration/age.
do you have uptime software (again a mitsi version software but works on the cat as its the same truck) or whatever the cat software is called.
id check that the ecm is seeing an input from maf, id check all engine inputs anyway, id check gas pressure which should be around 25kpa, id check air cleaner and the hose that comes from the air cleaner to the gas unit primary chamber cause if this gets blocked then the diaphragm will not work correctly and bog down like this symptom.
could be the small filter under the gas pressure sensor blocked,
could be an electric throttle problem.

that should be enough to check and eliminate some things and if I think of anything else ill be back