The "must" thing is hit and miss. The new shocks are longer allowing full range of motion on the shock. I ran stock shocks on my VX (mind you they are WAY different than other Isuzu shocks) and stock length ones (maybe they had slightly more travel, they listed them for 0-1" of lift at the time) on my '97 Rodeo with no issues and there are alot of guys on here that ran stock length shocks. The main issue will be extension, with the lift you'll be putting the shock closer to the end of it's travel. You could also shop around and find shocks cheaper (depending on the type you want) or even get just the coils and see how it rides without new shocks. If you like it, leave it. You'll eventually need to replace the shocks and when the time comes get ones with a longer range of travel.