Geezus scottie ... can you possibly come up with a more obfuscated way of doing this.
It's simple - your numbers - $1300 fuel, $702 fixed cost ... $2000 a week in cost. Revenue $1.31 at 2800 miles is $3668 in revenue - net is $1668
Hold back $.15 for maintenance reserve, $420 a week leaving $1248 for your pocket.
Take a week off and you net $548 the next week or split the week and net $900 for back to back weeks.
As for the residual ... you don't account for an event until it happens ... you either spend the cash when the time comes and depreciate the expense in the following years. Or keep the cash and finance the residual, write of the interest and depreciate the principal. Or turn the truck in and lease another. Or do as squeak is going to do simply turn the truck and retire off into the sunset.
All that said, the numbers you use have not been my experience... Fuel is close ... though for the past month I've not paid more than $3.29 a gallon. Fixed is $660, revenue per mile is $1.39 and over the past 4 years I've consistently run between 125K and 128K dispatched miles per year.