I know of more people than I can count that have have the exact opposite reslts. I have a xreas equipped 4runner, a friend has the 5100s. After riding with him I'm making the same switch. The 5100s are better in every way. Something isn't right here.
Swamp Rider, "better in every way" is a bit overstatement no? The extra body roll is not a minor thing IMHO... it's extremely noticeable w/o XREAS. I drove my Aunt's stock '06 w/o XREAS last weekend just to make sure I wasn't crazy. Sure enough, body roll and nose dives are there on hers. She doesn't notice it because that's all she's used to, and drives like an old lady anyway. To each his/her own - likely I'm a more sporty driver than most, but I for one feel the huge difference, and oh what NOT a feeling!" Test your buddy's truck out again and take a freeway onramp, curvy mountain road, or enter a parking lot driveway at an angle at ~5mph or so, and do so with a full Coke in the drink holder - I bet you'll find XREAS keeping the truck amazingly level while you're cleaning up the spills in the other

:. Perhaps new swaybar bushings would help some in my case, but I'm pessimistic how much.
Are you still running the stock coil springs? I kept my XREAS intact, but swapped out the stock coils for 2010 FJ Cruiser coils and it made a huge difference. I think that you might want to look at some coil spring options before spending the money to put XREAS back. I'm not saying that XREAS isn't good... I like it a lot, but it could probably save you several hundred dollars. I got the entire FJ set-up for $100. Just a thought.
I'm just really surprised to hear of your disappointment with the 5100's... people have been raving about them for a while. I agree with Swamp Rider... something doesn't seem right.
Yes, still running stock coils. When I initially switched I was going to go with FJ rear coils, figured I'd do those later when adding the air bags. But at this point I'm pretty set on just going back to XREAS. I haven't driven a full conversion (ditching XREAS / adding FJ Springs combo), but I have a hunch that adding the FJ SPrings won't do much for my main disappointments (body roll/nose dives/stiffness). Again, I guess the 5100's may be better for offroad?, but for on road I just don't see any benefit. The body roll & nose dives just kill it for me completely. Cost isn't much a concern for me. Stealership wants $2500-3k to replace the whole system, but I've searched a ton and for ~$1300 can get all 8 replacement parts, and will have a buddy help throw it in. I think I dropped $4-500 on the Bilsteins, had I known better I would've just replaced XREAS absorbers in the first place. The adjustable 5100's front are nice, but in hindsight I shoulda just gone with spacers.
Didn't mean to HJ the thread, I just hate to see here as in RedRacer's case yet another guy ditching a great system for what benefit? 5100's are really "better in every way??" Sorry I just don't see it, esp. when comparing to the benefits of XREAS. In any case, I'll probably have a set of 5100's with less than 5k mi. on 'em for sale cheap in the next couple/few months .. since everybody loves 'em so much doubt I'll have a problem getting rid of them

But SwampRider's right, if you keep the factory air in rear you'll need the HD's, else ditching that too you might find a decent buyer for the pump for that system, which I'm pretty sure isn't cheap ...