bigger tires recal speedo downshift way off..

[chevypower101]

ok I changed my tires from like 28" tires to 31.7" recalibrated my speedo and tire sizes now everything shifts fine but it seems when it should downshift it just sits in the lowest spot of the gear and almost doesn't have the power to accelerate and is unsure if it wants to downshift or try and make the power. why its doing this if your most likely wonder is because I have a 3.42 with nearly 32" tires. im sure i can tune it to make it work may run higher rpms and downshift to a lower gear at a higher mph than normal but im not changing rear gears. <----kma

 

I have a tuner and can adjust shift speeds but between the upshift and downshift the mph difference should be no less than _ mph?

[chevypower101]

also it the 4l60e 4 speed not the 6 speed trucks a 99 5.3 gmc sierra

[00Silverado4x4]

My previous truck had the same set up stock (265/70R17 tires and 3.42 gears) so I know it's not necessarily a power issue. I'd say get the transmission tuned (Black Bear or otherwise) and you should be good to go.