Pete 379 Automatic Transmission Conversion

I have been trying to do some research and am struggling to find any accurate information. I own a 1997 Pete 379. It currently has an 18 speed transmission with a Spicer 4-speed auxillary behind that. The truck used to have a lift axle but that has been removed. I have been toying with the idea of shortening the frame a little to make it more usable for the work we do. I was also curious about the options or possibilities of swapping the truck over to an automatic transmission. I would still like to retain the auxillary 4 speed. Someone had also told me they make some sort of auto shift that would fit on an 18-speed? Not really sure what options are out there and I don't really know of a good resource locally to reach out to for this since it is not your run of the mill style work. I figured someone on here might be able to assist with some different options I might have. Honestly don't have a problem with the current 18 speed it's just most of our driving is local in town and traffic and the clutch gets old after being in bumper to bumper traffic for long periods of time. Any help would be greatly appreciated. Thanks in advance for your advice.