2003 Chevy Cargo Van

2003 Chevy Express 1500 Cargo Van- white- has transmission issues. Previous owner was a mechanic and used this van as a mobile mechanic shop. Most components have been replaced or worked on. He told me that he had the transmission rebuilt at one point in the past. Also, he replaced the instrument cluster so the miles shown are not the actual miles on the van. I believe it has about 150,000 miles on it but the odometer says 170,000. The title says "not actual miles." I have replaced the starter and fuel pump within the past 3 years and a new battery 1 year ago. I used this van as a "camper van" and built a sleeping platform and storage section in the back. There is also a second or accessory battery and inverter in the back that charges while the van is driving so you can plug in electrical items. There is also an exhaust fan installed in the roof in the back of the van that is connected to the second battery. There is a back up camera and monitor. All of those were in working condition not long ago but now may need some new wiring/tlc, just like the rest of the van. It starts right up and will run but it has a transmission issue. When it gets hot it acts like it gets stuck in neutral and the engine revs but does not go. When this happens I pull to the side of the road, turn off the ignition for a minute or two and then start it up again. It will usually drive a little longer and then run into the same issue. I have found that leaving it overnight somehow it "resets" itself. At one point I disconnected the battery and restarted the computer and the van drove perfect for a long time after, but it has started acting up with the same problem again and it is becoming more frequent. I have spoken to mechanics who say it might need a new transmission, or it might be an electrical issue. Might be an easy fix, might not. I’m not sure and I just don’t want to have to deal with it. Text or email please.