First found the vibration at about 65-70mph with my 285s on, swapped some 245s on (different wheels as well) because I thought one of the wheels might be bent, out of balance. Vibration is still there, now just a 45mph. Seems like it is only in 5th gear around 1400-1500 rpm(this is with the 245s, never watched tach with the 285s). Any suggestions?

If you get on it some where you stay in 5th still does the vibration go away?
If gets worst I start thinking maybe the C3 clutch pack in the transmission is slipping some.

Brian

Man I sure hope not, not ready for tranny upgrades. To answer your question, driving slower or faster than 45mph it goes away. It actually begins around 40mph, is the worst around 45mph, fades until about 50mph when it is completely gone. Ive heard some talk about carrier bearing failure, but Im not sure of the symtoms.

Probably carrier bearing if your truck has one

My truck is an extended cab long box, I think that it has the 2 piece driveshaft?

Wish I could say. Seen what you described on a brand new 06 I was once was looking at. No idea what was the cause.

Brian

Most ext.cab long beds i've seen are only 1 piece shaft. maybe you had a driveshaft balance weight fall off???

Check the whole drive train ujoints cvjoints drive shafts you have to do the basics in the troubleshooting process also you cant totally rule out bad ballance on both sets of tires

First found the vibration at about 65-70mph with my 285s on, swapped some 245s on (different wheels as well) because I thought one of the wheels might be bent, out of balance. Vibration is still there, now just a 45mph. Seems like it is only in 5th gear around 1400-1500 rpm(this is with the 245s, never watched tach with the 285s). Any suggestions?


I've got the same problem, it starts around 40 and by 48 mph it's gone. I do have two drive shafts. It is hard to change our the carrier bearing?

how do you tell is carrier bearing is bad?

That sound like a problem that I have too.Do a search for "frame beaming" and compare to your problem.

First found the vibration at about 65-70mph with my 285s on, swapped some 245s on (different wheels as well) because I thought one of the wheels might be bent, out of balance. Vibration is still there, now just a 45mph. Seems like it is only in 5th gear around 1400-1500 rpm(this is with the 245s, never watched tach with the 285s). Any suggestions?


I would believe its a driveshaft issue. Cant say for sure though. With the smaller tires the driveshaft is turning at a higher RPM at a lower speed, which would explain why the vibration changed what speed it occurs at when you swapped to significantly smaller tires. I would also believe if the vibration isn't that bad it may not be noticeable at the higher RPMS that the engine would turn in a lower gear at that speed. But if its definitely only in 5th gear the driveshaft may not be the culprit.