When I originally put the 2.5 kit on I got about three inches in total height

 

While they may have sent you the wrong coils, skyjacker is crap. They shouldn't have netted you so little lift but that's why you don't see a ton of people clamoring to go buy those coils.

Contact their tech department and see if it's a snafu....otherwise......sell them and get some decent coils.

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I have a 2.5 coil spacer on my 2010 2 Dr and I'm wanting to go with a 3.5 lift. Would it be stupid to try and use the spacer lift I already have to add height to the new lift to make it 6" total? I'm fine with just having the 3.5 added but I figured if I already had the spacer that that I could just add it and get some extra height.

 

I see nothing about how you use the Jeep, or which wheels you got.
If it's mainly a DD, than why a 6" lift.
If you seriously offroad, than the tires are No.1 on the mods list.
With a JK, there's very little you can't do with 35" wheels and 2.5"~4" lift, not to mention 37".
Even an almost stock JK on 37"s is very capable.

A 6" lift on a JK may pretty much spoil the handling, both on & off road.
6" lift demands long arms and a list of other mods.

 

I have 35" duratracs with 4.5 back spaced rims. I'm thinking I'm just gonna go with the 3.5 lift.