It seems you have honed in on a particular issue -- your soffit vents are covered with insulation. But I would be cautious about isolating this specific problem -- it may not solve the bigger problem you are trying to tackle.
I am assuming you are hoping to deal with some comfort issues due to heat loss or heat gain from your attic area? If that is the case, I would recommend having an energy audit performed on your home to truly identify what your best next steps would be to stop heat loss or heat gain.
- Search GreenHomeGuide's directory for an energy auditor near you.
- I am not located in Nebraska, but it looks as though your state's energy office has a good deal of information on their website about creating an energy efficient home. You may be able to find a local energy rater through them to do an assessment of your home.
I would be cautious about creating any continuous air intake connections between your garage and attic space. With the few clues you have provided, there is a good chance you have some air leakage issues between the conditioned space in your house and your attic space.
- Opening your garage to this space as well could result in gases (like carbon monoxide) and fumes from your garage potentially getting into your home.
- A certified energy rater can evaluate your home and identify specific areas where energy loss and air leakage may be occurring and help you evaluate solutions that will give you the biggest bang for your buck.
For more information:
Read Jesse Terzi's Q&A "Should attic insulation extend into the eave soffits?"