340 Running super weird

Boy! Your question opened up a can of worms. You will receive about 1/2 right and 1/2 wrong answers.
Wait til the really “smart guys” wake up although RRR is about the best.
Honestly, without many many details we are just spitting in the wind and hoping it will stick to the front porch.
Way too many things could had been done. No details on what you have (stock or modified and how modified) is your drive train. Best bet is to ask for a new buddy locally that knows what the heck they are doing on here and get one pro from here to help you figure it out. You may just had had a leaking intake gasket or stuck distributor weights and now all heck has broken loose. Good luck.
Syleng1