Still overheating

my 74 has a funky overheating issue. its pissing me off. when i got it the rad was backed up. i tried 50/50 water and vinegar to clean the system i kept flushing it every time i drove it but finally got fed up and bought a new rad. it definitely helped i had to keep flushing out the heater core it was like a dumping ground for all the crap that was loosening up. so when it got to the point the water was staying clear i put 50/50 anitfreeze water. that day it started running hot. makes no sense to me, but it takes over an hour of driving, closer to 2 hrs, or strictly stop and go for it to get hot. im pretty sure i need a shroud and im working on one. you can pull the hoses off your rad and run a garden hose through the fill neck, you will be able to tell how its flowing. you can pull a factory overflow off a later abody