The only guys I have seen get off the truck successfully and move into on administrative only position had super squared away replacements to take over their routes. You need somebody that is going to maintain the same quality and reputation you have spent so many years building yourself.
You need to get that guy fully trained up in your methods, this may take years until you are comfortable letting him go out on his own. Once he does you are going to be sitting by the phone at night waiting for his calls, and they will come no matter what.
You are going to have to keep doing some of the work for a while, at the same time you will be monitoring his progress. You are also going to need to let him make mistakes, you can't be a helicopter boss always trying to make sure he doesn't mess up.
Be super strict about quality control, remember that it is your reputation on the line and one bad situation can ruin all of the years you have spent building it.
The other thing I've seen with guys that have done it successfully is they had an admin person, like a wife or daughter with some spare time. I haven't seen it done without this. Most greasers suck at admin. This will be the person that takes the leads, does the scheduling and handles customer complaints.
Maybe the most important thing with these guys is they gave the guy that was taking over the work the opportunity to make close to owner level pay, like whatever the ticket is, his pay plus whatever it costs to get the job done should be in the 50-65% range.
This may sound high but once he has fully taken over the route, you can now spend more time building up more crews, getting more sales, and learning how to manage the business better.