Re: Retaining the Nivomats
I've done it with 2" spacers and 2" shock extenders and it's worked fine for the last 7+ months or so. I tow with mine too. The extensions effectively adjust the neutral point of the shocks in accordance with the new higher ride height provided by the coil spacers.
http://www.tahoeyukonforum.com/forum/showthread.php?t=52533
The Nivomats "want" to be a specific average length as you ride down the road. They are paired up with coil springs that are much softer than what you'd find on your vehicle had it not been equipped with the nivomat shocks. They are a load bearing suspension component unlike traditional shocks. If they're too short on average they will "pump" themselves up until they are back to the length neutral length that they want to be (Lifting the rear of the vehicle). If they are too long they will provide less and less support and try to get back to that neutral length (Lowering the rear of the vehicle).
The problem you might have with the spacers that the Nivomats may work against your 1-1.5" lift goal without shock extensions specifically made for either a 1" or 1.5" lift spacer. Most, if not all of the shock extenders I've seen on the market are either for 2" spacers or they don't even specify the amount of extension. With the conventional shocks on the rear you can usually do 1" spacers and keep your stock shocks and no extensions. What might happen with the Nivomat load leveling shocks if you don't use extensions is that they may lower your vehicle back down 1" after you put in the spacers by providing less and less support until the shocks reach their predetermined neutral length.
If you do add extenders that are actually for a 2" lift but only want 1" of lift the nivomats may "pump up" and effectively lift the rear of your vehicle up to that 2" mark.
I can't comment much on the front lift on your vehicle as my generation has a torsion bar suspension and is lifted in a quite different manner. I noticed no handling or ride quality differences when I lifted the front of mine 3" and swapped in bilstein shocks.
In short: your resulting rear lift height may be more determined by the exact length of your shock extenders than your lift spacers with Nivomats. It would be very ******* the shocks so I wouldn't do it but I'd bet I could remove my spacers completely and still have 2" of lift in the rear of my Yukon from extending the Nivomats alone.