850 Carter Thermoquad flooding at low rpm

I am not a mechanic but mechanically minded and looking for an understanding and solution. The car (had it about a year) has a 440 with 460-500hp, Carter 850 carb, with a Mopar Purple cam 296/.557. Overview….. Car fires up and runs nice. I had always noticed after going for a drive it idles rough at stop signs, and couldn’t put my finger on it, but it came to a head yesterday on a long slow drive. I live in rural Nova Scotia Canada and took my wife for a nice long drive along the coast. I probably drove the coast line for 2 hours at 1500rpm 40-45mph. After the first hour I noticed the car getting rougher as we cruised ( the tack would pulse periodically). Temp is solid 180. At the end of the 2nd hour (about 90% of the cruise). I stopped at an intersection it started sputtering badly and it was all I could do to keep the car running. I pointed the car towards home (1+ hrs)….. yep, we are in **** the bed mode. the car kicked and sputtered for the first couple miles and as I picked up the pace it felt a bit better At 2200rpm (once I got it there). The last 1/2 of the drives the car started to feel better. When I got closure to home (and braver) I gave the car a couple of good pulls and every one was better that the one before and when I returned home the car was running normal. I suspect that the fuel supply is too heavy at lower rpm and flooding the car. Looking for thoughts and education. Thanks in advance RonD
Update on the carb issues. The car is now running fantastic. I took to an engine builder at R&D Performance Nova Scotia. He reworked the distributor, replaced the vacuum advance. It appears the issue was not dirt in the carb, but very low vacuum pressure. Thanks for everyone who took the time to provide suggestions. They pulled me in the right direction. Ron D 71 Swinger (aka “The Gypsy Queen”)