I had this problem with mine from brand new.
YOU MUST DO BOTH ENDS.
I'll repeat that, you must do both ends - as I found a lift on the rear transfers more weight onto the fronts which stuffs your front alignment - the front wishbones run a 2:1 ratio, so if you drop the front end by 20mm as the spring compresses you are already into negative territory for the front wheel angles. What happened to my ute was the front end would just wash out left or right on gravel and you couldn't steer out of it. Bloody dangerous and pretty terrifying as you couldn't correct out of it.
I had my leafs done from the dealer, as I was writing off tow balls on driveways and sitting on the bump stops... Front end they walked away from (thanks Ford).
My solution, was this from Iron Man at the front:
Ford Ranger PX Front Strut - Foam Cell - Ironman 4x4 - NZ
This has a separate spring seat which slides right off. This allows you to tune the front ride height by inserting a spacer ring under the spring seat, and with the 2:1 ratio a 10mm ring gives 20mm lift at the front end. If you go to an adjustable strut with locking rings - you have to cert the suspension as it's modified. Because the Iron Man strut has a solid spacer ring, it's not adjustable so that means you don't have to cert it. These struts can be used with the factory springs = a cost saving. Do the rears with the same branded shock offering.
Springs I had were from the Cambridge spring workshop, mine are a 7-leaf with overload which compares to a 3-leaf factory with overload. I carry about 225Kg as standard load, and I could probably afford to go to a 6-leaf+overload. My standard lift is about 50mm at that weight, max for uncerted mod but that part was a dealer fit so didn't need certing... The front dropped about 22mm, which is where I arrived at the 20mm lift figure with the 10mm spacer ring under the spring seats.
To be honest, the difference for me was chalk and cheese, turned a useless piece of crap expensive lemon into a functional work ute, got 85,000km's on them and I haven't looked back the Iron Man product has functioned exceptionally well...
Add a note - I didn't have to touch brake lines or any other bits, driveline angles are steeper and did concern me but no issues as yet. I have noticed that the traction control and vehicle safety systems like ABS are a lot more gentle and come on a lot more progressively than on factory suspension, they came on with a crack when the ute was on factory but now if they come on the vehicle stops doing whatever was naughty, the light comes on on the dash and you keep driving - that part of the mod was awesome and a vast improvement.
