geem

New here hope someone has any answers. 2011 Rav4 2gr-fe v-6 flashing cel pulled codes p0301 & p0300 and sometimes p0306 . flashing cel only occurs in 4th & OD . leaving the rav in third and staying below 50mph no issues ( this a 4+od auto). New plugs , coil packs , pcv,cam position sensors,vacuum hoses , cleaned MAF and throttle body ,new injectors. Installed an additional ground strap to the engine & code disappeared for a week then returned . Could this be an ECM issue ? jumper cables were connected backwards one time on this vehicle ,no burnt fuses. Any ideas ? Dealer was no help. Thank you