are there any problems with the rear suspension?
can they candle 600lbs of tongue weight and full passengers?

 

I've never heard of any problems on the 03-06's IRS.

 

I've towed quite a bit and hauled even more... And my rear end was replaced at 56k... I can't say if I made it worse towing, etc. as this was a known issue. I haven't had any issues with the IRS per say, just the differential.

Towing 6500 lb travel trailer w/ WD hitch, 3500 lb boat, 4x4 trails, etc...

2004 EB 4x4 model...

 

No one I know with a 4 x 4 Expedition, has made it past 70,000 miles without needing a new rear end, or a new transmission, or both...

However, everyone I know with a 4 x 2 Expedition has not had a single problem with the truck...

4x4 seems to be a POS in the Expedition line...

Coincidence? I think not...

 

are these 9.75"?
is it the limited slip that's not dependable?

 

Our 2000 XLT 4x4 /w 5.4L was still going strong at 95K. But that was the 4R100 transmission and the larger rear end (no limited slip). No IRS though, it had a solid rear axle.

 

Mine is the LS and 9.75" rear end. The size is the same, but the housing is different to accomidate the IRS. I was told the new parts are much more rugged than the old ones... We'll see how it goes.