Gnostic's believed in hidden knowledge. I think most of the dispensationalist publish who they came to their understanding of scripture and really don't feel like they are part of a chosen few who have special revelation etc. No we are not gnostics in any sense. Marcion Heresy isn't really will understood because most of the tests are lost except for criticism of it. My understanding is that they denied the God of Abraham. Isac and Jacob and the relevance of the Old Testament Scripture. Most of the dispenstionists also use Old Testament Scripture as I did to validate my beliefs. I think calling a belief a heresy with out really understanding the heresy is a little strange!
I don't think you're a heretic. I think you're smart enough and well read enough to start digging when and if you realize how close dispensationalist doctrine is to that specific heresy. I also think that among all the dispensationalist and Rapture focused folks I know as well as the majority of Protestants I've ever known, it's actually interesting how much they're all focused on Paul, just as that particular heresy was.
I know it's dispensationalism isn't Gnostic although the entire marketing of it and the Rapture focus on engaging the mind the way Gnostics say is the only way to Salvation and knowledge. Rapture folks are just doing it out of some coincidence, not because they're Gnostic.
I'm pretty sure you're not Gnostic. I don't know that dispensationalist doctrine and the rapture that flows in part from that doctrine are much different in the way they approach Scripture. If fact I think it's a very bad indicator that they are so close to it in their approach to and use of Scripture. Like Luther adding “alone” to a verse to support his own theology. I get very worried when something begins by tampering with Scripture since that's how all cults and heresies start.