[71gtx]

Well i have a 340 in my plymouth. I noticed whenever i drive now that if i keep the throttle constant i feel the car trying to rev and then kick down and rev and kick down. almost like a chug, but not so much, like its trying to kick back and forth from going constant to going faster.

then i just let the car sit in park and i went to the tailpipes and listened, and it even did it in park. the exhaust would be constant with occasional high revving additions. its kind of hard to explain so any advice would be appreciated. thanks

[NorthStar]

Sounds like youre describing a surging condition to me.
Check this out.

http://www.recarbco.com/technical/smog/smoginfo.html