I know I've said it before but if you have too many jobs where you are losing a couple due to time constraints...just find a local quality carpet cleaner who isn't as busy and as him to help you out..sub a few jobs to him/her so you don't lose the entire job ...or customer....and then when you have some good money in the bank, take the next step.
Adding another truck takes revenue so you need to take steps to obtain some. It sounds like you are too busy to spend money...which is a good thing...and should be putting some away.
Just don't bust your whole nut when it comes down to it...You always need to have some "oh shit" money.