99 Suburban 2500 shakes at 65-70mph

[Stevodod]

I'm about to take my 1999 K2500 on a cross country trip, it runs fine but it shakes pretty bad at 65-70mph. I've had three sets of tires on, had it balanced, aligned, shocks replaced, all new brakes, the works, so it's NOT those simple fixes.....

I'm thinking motor mounts, rear ball joints, or something else.

I did rebuild the engine and didn't put the transmission cross mounting bars back in (2500 series only). Every service tech says that shouldn't make a difference.....

Thoughts?

Thanks,

Steveo

 

[zora]

if you shift into neutral at 65-70 and let the engine go down to idle does the vibration stop? if it does you have an engine related issue. If it makes not difference you may want to look if the driveshaft has been damaged in some way.

 

[Chuzz]

Is it four wheel drive or two wheel? If it's four wheel drive, it sounds like you've got a bad axle to me. If it's two wheel, then I'd suspect a suspension part. Perhaps a bad bushing, but it seems like you'd notice it at any speed if it were that.