Gear Down Setting's

[superbudy208]

I was wondering what the best gear down setting would be? i thought my truck was going in to derate but somewhat fixed that problem and just got looking around into the settings and found my gear down under heavy engine load was 61 and light engine load was 58 mph, and thats right where it does it in 9th gear trying to keep the rpms up, was looking for some insite on where to set it a? 08 pete 387 cm871 10 speed ultrashitter auto. just tryiny to keep the rpms up on the hills and truck will run 58 at 1550 rpm's will go to 61 then back down to 58 and shifts very early into 10th. any help would be great, thanks