The kit is new with all the rollers. Locking tools are essential? It has openwork marks for camshafts and crankshaft
the marks are for basic alignment only, and not for the fine adjustments needed to get the timing correct. It's very common for all 4 cams to be whole tooth out if done without the correct tools. Which are:
A crank 'lock' which wraps around the water pump snout, but isn't intended to undo any of the bolts
A pair of wedges, each of which hold one pair of cams in the correct position once you've checked that with
The alignment gauge, which is the most important part of the set.
Once all 5 toothed pulleys are locked, you remove and replace the belt and rollers, ensuring that the belt is adequately tensioned and the 3 adjusters are in the centre of their travel. Then you remove the locks, turn the crank through one complete cycle, reinstall thd crank lock and gauge, and adjust the tensioners again. You keep doing that until they don't need adjusting. This is the attention to detail that if omitted(and it often is due to time constraints or ignorance of what's actually required) that can cause big problems. An experienced DIY mechanic ought to be able to do his first V6 belt properly in about 90 minutes, so it isn't too horrendous