I have a 2001 manual, VU v6 Ecotec Ute, which is all stock apart from 2.5 CAT back and CAI, it has a terrible low end torque, I have about $500 and looking for 25mm manifold insulator,12 mm plenum spacer which will take me to 370 but not too sure what els

This combo, especially with the larger throttle body, will considerably increase bottom end torque. Resulting in the vehicle being much more responsive at lower engine RPM. The manifold insulator, plenum spacer and larger throttle body will genuine give gains on even a dead standard vehicle. The fact that you have a manual VT-VY V6 means that you don't have to upgrade the computer to suit the larger throttle body either. While our higher ratio rockers provide solid gains, they tend to be around the mid to top end rev range. Given you're after greater gains in the low rev range, I would recommend our manifold spacers first.