Been chasing a stumble in the 7000 rpm range at 2700-3000 rpm for years. Blamed it on the last ecu refresh back in 2015 I had done to resolved the cold start issue, haven't had any of the latest ones fear of all the bad reviews making some sleds worse. Decided to Go through the sled this year, replace bearings and grease what needed grease but in relocating the fuse box and upgrading to sealed relays I checked the ground from the wiring to the chassis up at the top of the belt guard above the primary and it was super corroded. Took everything apart, cleaned and reassembled with dielectric grease. Guess what? Stumble is gone, completely. So if anyone else has it in their 7000 engines better check the ground connection.