06M6QSMGoat

Just bought my LS2 Goat and found out it had a cam, and boltons and at one point had nitrous. Bought from a dealership drive home and did awesome no problems what so ever. Got back in town put 91 in it and it threw a CEL which read to be "rich banks 1 and 2" come to find out Previous owners friend told me it switched back and forth between E85 and 91 tune. Had a buddy hook it up to HP tuners and the LTFTs vary from -12% to -6% pending on the cell and under WOT it shows around a 12.4 AFR on the factory 02 so I'm not sure whether it sounds like it's on an e85 tune and running rich on 91 octane or if it sounds like it's on a 91 octane tune. Also sometimes after it's been sitting a while it starts and bogs down then revs itself up to keep it alive then will idle just fine with no problems. Any help would be appreciated