Strange Issue With Tune in LS-Swapped 66 Nova

Hi all, new to tuning and not sure what my car is doing. Back in December I did a cam swap in my 4.8L LS-Swapped 1966 Chevy II Nova, then had a local place tune it. I went to the track a couple weekends ago and noticed at full throttle around 4300rpm in 3rd gear, it drops down in rpm then recovers. It was at that point that I decided to get HPTuners to be able to data-log what it's doing wrong. I attached a 0-90mph pull which demonstrates the issue. It is visible in 3rd gear around 80mph

Next time you Scan add delivered engine torque, MAF in Freq, and cylinder airmass. I do not know what caused it but those will help. Log oil pressure too.