Yeah I haul around 500-800 lbs of mulch in my '98 every spring (though centered in the cargo area so the front suspension takes a bit more of the load than if it were a trailer), plus had the typical rear end sag, so Monroe Load Adjust shocks have left my '98 sitting maybe 1/2" over stock height after 6 years, and have done their job except for three factors.
1) Bumps and potholes are far more noticeable. As when the suspension was factory new, it rides better with a load in it.
2) The extra strain on my lower shock mounts, along with ~22 years of rust, caused them to fail. They still held the leaf springs when their ear that holds the shock mostly broke away, so it wasn't catastrophic, but if I had to do over, if those lower shock mounts are rusted much then I'd go ahead and replace them before adding coilover shocks, or new air shocks.
If they are rusted much then you may need the axle U-bolts replaced too. That's not very difficult or expensive to do, about $55 for the lower shock mounts and $25 for the U-bolts, except again, rust, so I cut the U-bolts off with an angle grinder.
Also once that lower shock mount breaks loose, it's not a lot of fun trying to get the lower shock bolt off since it's then not firmly held by anything. It's easier to just undo the top shock bolt and take the shock off with the piece of lower mount still bolted on, to get it off in a bench vice.
3) My upper shock mount rail (goes across the whole frame) is eventually going to need something done to it too, is rusting slower due to being up higher, but there is no Ford (or aftermarket AFAIK) part to replace that, would have to be fabricated from scratch. That's not too far out of my wheelhouse but getting the dimensions right could take some trial and error.
