Well. I run a 48x96 reefer. For the most part I have no issues getting lOaded. Don't tell them you have a 96 though. That just scares them. The only thing I see is that I don't sit around places like company guys do. So as far as I'm concerned you can keep those 53 footers.
I use a specialize 48' with a aluminum floor to haul animal feed and some auto parts shipments that are stackable containers - thats it. Get a 53'.
Thers plenty of freight for a 48 footer. When i had a van 95% of the loads did not even take the whole 48ft. Just because the broker or shipper ask for a 53 foot trailer does not mean they need it. Have had shippers ask for a 53 and show up with a 45 footer and still have room. The main thing is to know what your hauling. Dont book a load of toilet paper with your 48 and exspect it to fit.
There is a difference between if freight can fit in it and what the shipper asks for. Other issue with 48' dry van is a broker who is looking to grind you will use that to keep the rate down. You just put yourself on the wrong end of the supply and demand scale.