im going ot on a limb here bt maybe at that speed the trailer is flexing or the suspension has a problem maybe even a bent axle and at that speed is the only time you have a problem

 

Damn thing better not be messed up I just bought it its a brand new 5thwheel spent 35k if its bent I'm gonna bend the dealer

 

Not knowing squat about diesels, but based upon the symptoms and the onset (only 1 trailer and only at a certain speed range), I'd have to agree with the above post.

If it were consistent with any trailer, then I'd be looking at the truck.

In this case, I'd be looking seriously at the trailer and rigging

 

Well it did it again this morning but this time with a 30 foot flatbed with nothing on it. You know how if you miss a gear and go from second to 5th how the truck will jerk almost like its stalling out well that's what it feels like to me I'm totally lost here. I really don't like what its doing I'm afraid its gonna break somethin soon

 

Is it only doing it with the trailer? If a problem like this presents itself, It's generally truck related. It's hard to say with the info we have about your truck. Do you have gauges? We need some data to help with a diagnoses.

Boost Pressure
EGT's
Fuel Pressure
Smoke and Smoke Color
Unusal noises
Burning Oil?
Leaks?

There's millions of things that could be wrong. To help we need the data listed above!

 

so its only in 3rd gear with that 1 trailer? maybe 1 of the trailer tires is out of balance?

 

Its only in third gear between 2200 and 2500 rpm. At 20 to 25 psi egts are around 900 to 1k light haze no oil or fluid leaks to speak of and so far its done it with 2 trailers a 40 foot 5th and a 30 ft 5th the 30 was empty and only wieghs about 4500 pounds the 40 weighs about 18k loaded with my crap the jerking just started out of nowhere after I got this 40 footer it didn't do it when it was empty but the minute I loaded it that's when it started I pulled the 30 footer a million times and it never did it until this morning. Even when I pull my 32 foot rv wich is a bumper pull with 3 quads in it its never done this. If it was jerking in all the gears I would say clutch but its not only in 3rd between 2200 and 2500 rpms that's why I'm lost here

 

try giveing you gov springs 1 more click

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before you do that ... when you put the springs in did you give them both the same amount of clicks?

 

I micd both of them when I put them in with a caliper and set them exactly to where the stock springs were per the instructions is it possible for one to work loose

 

is anything done to the tranny?