okay this might be long but here goes.
So today i was driving down the freeway with cruise set at 80. Was climbing a hill and the cruise could not keep the truck at 80 so it decided to kick down into 4th then the truck slowed way down to fifty and the check engine light came on.
I tried accelerating again and the truck would not rev over 1900 RPM's no matter what i tried. The truck would not go over 70MPH and the only way i could get it to rev over 1900 was to put the peddle to the floor but then it would downshift and then slow back down to fifty again as if it was stuck in 3rd gear.
When trying to accelerate it would sputter and not speed up unless i barely gave it gas. I have no idea what the problem is and i let the truck sit for a couple hrs and got back in and started it and the check engine light was back off
Any ideas??

Sounds to me like it went into Limp mode. if it kicked out of O/D at 80 the RPMs probably jumped up pretty good. You'd have to check for codes, but I wouldn't be surprised if it was a overboost condition.

Was the truck running normally after you went back to 2 hrs later? most likely you won't have any adverse affects, just a protective measure in the ECM

when i went back and drove the truck a couple hrs later if i put it to the floor it would still sputter and not rev over 1900 for awhile than after a little bit it would rev all the way up.
Also the turbo sounds louder and almost sounds like its whining not whistling.
Its hard to describe but it just sounds like something isnt right. I may just being imagining things but im not sure. Also once i was driving for awhile and beat the s*** out of it for awhile it seemed like it started running better. Also once i got back home i let the truck sit for about a half hr and went back out to put it in the garage and it cranked for like 10 sec before it would fire.
I just dont think its limp mode cause i have put in in limp mode before and it would still let it rev over 1900.
Hopefully tmrw i can get the scanner and see what it tells me.

I would start simple first and change the fuel filter. I am not a mechanic but it sounds like it could be a fuel delivery problem. At best it will work, at worst it will probably be part of the repair process anyway.

The dirty fuel filter threw a fuel rail pressure high voltage code P0193 and that caused the motor to overboost(so says the computer). mine did the same thing.

the same thing happened to me a while ago. i pulling a 8x10 trailer with two wheelers on it, should be no prob for the dmax. going down the highway it just started down shifting and going slow. when i tried to get back into the gas it made it go slower. so i took back roads home going stupid slow. when i go home i unhooked the trailer and tried it back on the highway, when i smashed it it haulled ass like nothing was wrong. there was a engine light on still though. tried the trailer again. no go. i thought to change the fuel filter and the air filter. i went to my buddies house to do the filters because he had the 4'' exhaust that i bought. when i got there diesel was pouring out from somewhere even without truck running. went to the stealer that night, injectors.

x2 on replacing the fuel filter.