Last time gas hit $4.00 plus a gallon, truck sales tanked. Place your bets gentleman.
People who buy trucks don't buy vehicles often, due to initial cost and trucks' excellent durability. They'll put up with auto insurance costs (trucks and larger SUVs are often thought to be inherently safer, which is important to parents of children) and cut miles driven if the price of gas becomes a problem. More likely they just put up with it. Parents who don't want their kids riding the school bus (I can see why they might not) or are not in the service area (we were not, enormous rural school district) cooperated with school transportation, and I'm sure that's still done, even in the two-career era.
There is always a pucker factor when there are big increases at the gas pump. I don't think $4 gas would have the same impact today. I am thinking it would be above $5. Auto and trucks get better gas mileage today. The credit crisis also had a major impact. Credit dried up. There was noway that people in debt with their credit cut off to afford gas.