Slow crank

Think about this. The original +ve battery cable is about 3 ft long . The new cable to the trunk is 12ft. If it is the same gauge cable, there will be 4 times as much voltage drop; if it had 0.2v drop, it now has 0.8v drop, voltage that is lost & cannot contribute to providing current to the starter.

Another way of looking at it: the new cable needs to have 4 times the cross sectional area of the factory cable to keep voltage drop the same. Think how much extra weight that is that the car has to move.............& you have just spent $000s on a more powerful engine to make the car go faster. Although more grounds will 'help' they are usually short lengths, when the real culprit is the long length of +ve cable.

This is a good example of why having the battery in the trunk is a bad idea, unless reqd to do so by some rule or regulation.