The purpose of gap insurance coverage for your commercial trucks is to protect the lender or the company you are leasing your commercial truck from incurring any losses if you truck is totaled.
Gap insurance works with collision coverage and Comprehensive Coverage
For example: If you owe $50k on your truck and it is totaled. And the insurance adjusters pays an actual cash value of $45k. And your deductible is $1k. You get a check for $44k. You would look to your gap insurance to makeup the pay the $4k difference bringing the total payout from your insuring company to $49k.