i have a 97 XJ sport, 3.5" Tuff Country Lift, 1.5" rear lift shackles, front lower BPE, rear upper BPE, 31x10.50 BFG all terrains.  the lift kit i have now lifts the rear with blocks. with the added weight of a new bumper/tire carrier, i added the lift shackles to accomadate. my problem is the stock rear leaf springs. they appear to be de-arching. after driving it, the springs look flat and when it sits for a while, they sag. i want to take the lift blocks out and install new springs, at least 2.5" lift. a friend of mine has a set of skyjacker leaf springs, brand new, 2.5" lift. are these any good? is there any other companys that sell just the leaf springs with a lift? is there anything i should be concerned about during/after the installtion of new leaf springs? i already have a SYE and driveshaft, so vibrations and angles are taken care of.  

More than likely they are going to be a soft ride spring that is not set up for a tire carrier and you will end up in the same situation .