You have a job that requires you to travel up to 300-mile round-trips where they expect you to use your own vehicle and only pay $55k for someone with presumably a college education?

If they're not providing a company car + gas, or reimbursing mileage, you need to find another job ASAP. The IRS government reimbursement rate for business use of a personal vehicle is $.655/mile. If I conservatively assume you are doing 100-mile round trips daily, that's something like 2,000 miles a work-month or $1,310 after-tax that you're being shorted if you're not being reimbursed. If that's the case, no wonder you're falling behind.