I think you have a weak fuel pump. The reason it starts acting up at highway speeds is probably because it cant get enough fuel to run right. These old trucks with no overdrive turn some high RPMs on the highway and high rpm = high fuel consumption.
You probably had problems with the truck getting up into the driveway because it was cold. With the choke held open with the screwdriver the engine wont be getting a rich fuel mixture which it needs while it is cold, not just while starting. I have to start my carbed vehicles 2 or 3 times when its cold before they will even run long enough for me to rev them up. Then I have to hold them a 2000 or 3000 rpm for a couple minutes before they are warm enough to drive. Thats because I took the choke off of them... lol.
You will have to let the truck warm up a while before you can move it with no choke or a malfunctioning choke.