I have a slightly different perspective on the Frontier suspension, for what it's worth. My 2005 Frontier is my commuting/pickup truck vehicle; it's not my "Expedition" rig, so I didn't initially invest in a high quality aftermarket suspension. I purchased a Calmini 2-2.5 inch/1.5 inch spacer/shackle kit (don't know how different it is from a Readlylift although I think the basic concept is similar). It seemed to do an adequate job but I always noticed that hitting potholes/etc at speed (particularly highway speeds) would sometimes give a feeling of instability in the front end of the vehicle. Now, this year, I noticed that the ride was increasingly rough on the post-apocalyptic highway to our house and the rear was sagging, more on one side than the other. Also, a fairly minimal load (around 150#) in the bed resulted in about one extra inch of sag. After a fair amount of research on the Frontier (and FJCruiser ) forums, I have concluded that:
1) About 2-2.5 inches of lift without aftermarket upper controls arms results in UCA/Coil bucket contact. In fact, aftermarket UCAs are recommended with that amount of lift.
2) Various methods of obtaining lift in the rear (spacers, shackles, Deaver Add-a-leafs) result in premature flattening/sagging of leaves and, presumably, loss of suspension performance. My Frontier only has 37K miles on it, as well.
3) "Leveling" is probably not a great idea in any vehicle that is going to be loaded with anything; either expedition vehicle or pickup truck, because any substantial load will bring the back down and the nose-up condition is way worse than the nose-down situation (effects on handling, shining headlights into oncoming vehicles, etc)
Consequently, I purchased the following:
1) Radflo 2.0 inch adjustable, extended travel coilovers (for 2-3 inch of lift), adjusted to about 2.5 inches. Adjustable coilovers, I think, are indispensable for dealing with the inevitable lean (usually driver side lean) that occurs in these vehicles.
2) PRC Upper Control Arms. These were relatively modestly priced but appear to be doing the job quite nicely.
3) Alcan Custom (replacement) Leaf pack with 2.5 inches of lift and @400-500# of extra capacity. You can order whatever lift (up to 6 inches), and extra capacity you would like. It has @8-9 leaves, as opposed to the three that come with the stock suspension, which I understand to be superior for performance and longevity.
4) Bilstein Rear Shocks. Fairly generic, although I was tempted to pick up the Radflo ones.
These were purchased from PRG in California (except for the Alcans, which were purchased directly from Alcan). I spoke with Greg at PRG on the phone and he helped me configure the setup to my requirements. I would recommend PRG based on my experience. I think of the setup as being mid-range although it definitely wasn't cheap, especially given the custom leaves, but it should last the life of the vehicle. This setup will also make this vehicle more capable if I decide to use it for something other than its current application. I'm happy with the way it handles on (and off) the road now and I'm happy with the look of the truck, even though I kept 265 tires (didn't want to mess with trimming any fenders, often necessary when you go to 285s or bigger). Those are Goodyear Duratracs, FYI. Hope this is of some help to you. I'm not saying this is THE suspension setup for your needs, I just think there are some things that I learned along the way that may help you make your decision.
