Unusual toilet problem

I have a 2014 Fleetwood Storm 32h. This is our first real trip and the toilet was fine for the first 2 days. On day 3 my son told me the tank was full because it wouldn't flush after his #2. I thought it was unlikely to be full after such a short time but we have full hookups so I would just dump it. Everything seemed to dump fine. I went to flush with the chemical in the bowl and it wouldn't flush. I saw a clog right behind the valve so pushed it through with a stick. I then pit about 8 to 10 gallons of water in the tank to compensate fir the ball of tp. Later the toilet just wouldn't flush correctly. Every time I would flush it would burp back water before the contents went down. I dumped the tank and the same thing would happen. I guessed that the vent was clogged so ran a hose to the roof vent with the dump valve open and found that the vent stack was pushed up about 3 to 4 inches too high which actually tore the cover right out of the roof. I was thinking that the only thing that would do this is high pressure in the tank which caused the tank to bloat since the vent would be through the top of the tank. I ran water down the vent pipe and it went down into the tank and out the hose without issue. I then closed the dump valve and began the tank rinser and could feel air exiting the vent. I think the vent is open. Currently the only time that the toilet flushes fine is when the dump valve is open. It keeps sounding like it's the vent but it's open. Any ideas?