1999 shake when towing

I have a 1999 Silverado ext cab long box 4X4 with a 5.3 and auto trans.
When I am towing a trailer, there is a really noticeable shutter as soon as I start moving from a dead stop. This truck has a 2 piece drive shaft with a hanger bearing. The shake stops by the time 2nd gear engages.
The U-joints seem to be in good shape. I can flex the rubber around the hanger bearing by pulling on the driveshaft side to side. Its not sloppy, but 1 or 2 of the webs in the rubber are broken.
There is also a slight resonating shake on deceleration when empty, but it is barely noticeable.
Could this be the bearing or somthing else???
K

Well here is my FYI for yah:

I have this exact same shudder in which you speak and things I can tell you it's not are; U-joints and bent drive shaft. From everything I've read if you go to a one piece drive shaft then the shudder goes away.

I've had all three U-Joints replaced and my main Drive Shaft balanced all to no avail. Almost $700 CAN to have all that work done and still the mild vibration. I'm not sure if it's that Hangar or not but, I think I may throw some Shocks on it to see if that helps at all.

Let me know if you find anything out!

Evan

I have a 99 2wd xcab short bed, had the shudder empty and after putting a slide out camper on the back the shudder was really bad, had airbags installed and the shudder was gone loaded or empty, air or no air.. not sure what the reason is but its fixed..

Had the local driveline guru over to have a look at my truck. he said to check the joint directly behind the hanger bearing and make sure the slip joint slips properly.
He also told me when loaded, the pinion angle on these trucks change quite a bit which can definately cause this type of shake, so I think mec's cure with the airbags may be the proper fix.