^ heaten by jdk, but my response was predictably wordier, because I have too much time on my hands.
None at all.
A shock used with 2" lifted springs must the approximately the same length fully compressed as a standard shock, otherwise custom mounts or bumpstop spacers would be required to prevent damage to the shock or mounts. They will fit and work fine.
As an aside, many aftermarket shocks sold for sierras actually have less travel than the standard shocks. They are typically a little longer fully compressed, which makes them a little bit longer fully extended. Increasing shock travel more than about 25mm from standard requires work to be done to the car to fit the extra compressed length in.