Brandon2013!

So I’m pretty much stumped at this point, I got a 2009 Silverado 1500 5.3L I had a flashing CEL at cruising speeds suspected it to be the afm issue so decided to buy an afm delete kit. Put the kit in everything went well motor runs great but still same thing.. truck runs great if I’m getting on it or getting up to speed but as soon as I get into 6th gear cruising check engine light starts flashing and I’ll floor it and get it to up shift and it’ll go away. I had it retuned twice thinking maybe that was the issue, there’s code po3401 which is something to do with 4 cylinder mode but won’t stay off after turning it off in the tune..