Chevy & GMC Vans

I drove the van about 40 miles round trip yesterday with visitors from out of state. It's always when I have passengers that I notice anything poor about the van. This time it was vibration problems.
The tires are 30k old. The IAS Edelbrock shocks are over 100k old, but show no signs of leaks or bounce. the steering parts are 160k old with the upper ball joints and idler arms recently replaced. Wheel bearing are fairly new as well.
Any suggestions on what it might be, how to check for it, etc? And no, I was lazy and have not done a search. Sorry.

U Joints ?

If you have aftermarket shackles on the leaf springs...you probably had just the right amount of weight in the van that the pinion angle was "just so" and caused vibration that you don't notice otherwise.
That's one possibility anyways...

Could you please tell us where you think it is coming from??.Front,rear,left or right side??.That might help.

I notice it at freeway speed. I sometimes think the freeway is uneven and therefore I feel the up and down rolling road, but after such a long drive, the entire road can't be like to blame. I'm wondering if the tires are wearing poorly and uneven and causing this vibration. I'll check the ujoints as suggested, but haven't heard any clanking or such. I also wonder if more "steering knuckles" needs replaced.
To add further fodder, I worked on a friends 2000 Jeep L6 4WD Grand Cherokee this past weekend. What a nice riding vehicle, tight turning radius and smooth ride (stock). Much better than my Astro! I hit speed bumps like they weren't even there. I already upgraded so much on my Astro, I wouldn't even know what to improve to reach the ride of the Jeep.

bump

bump ??? What does that mean?

What have you done/checked?

Keep us posted on your progress.

Jim

PS If you really want your Van's ride to exceed that of the Jeep's... Pull the lift and big tires off, and get back to a Stock Configuration.
Just my opinion...

I did an inspection this weekend; motor mounts, steering linkage, ujoints, shocks, etc. Everything looks great. I repacked my front wheel bearings too. Although I can't tell, maybe my wheels are off balance. My next trip is to the tire store to have them checked, maybe that's all it is. I hope so.