[ChevyHighPerformance]

One thing to keep in mind is that as you increase the height of the front of the vehicle, the front axles/CV joints become more misaligned. The efficiency of the CV joint drops as the ends become more off axis. This increases your drivetrain losses resulting in less power to the wheels and lower fuel economy. This is the same philosophy as setting the proper driveshaft and pinion angle or torqueing a bolt using a universal. This may not may the complete cause of the issue here though.

For example, the Corvette (IRS rear) has about 2% worse drivetrain loss than an F-body (solid axle) due to the 4 CV joints in the Corvette's IRS.