Over reving

[Dannyboy]

When I have my boat hooked on the back (8000 lb) the truck seems to over rev after coming up a steep grade, and when i shut tow haul off it seems to quiet right down unless i stick my foot into it. Has anyone else noticed this?

[Jim Brzozowski]

If I remember correctly, the computer determins the upshift point based on the current gear running, and gear selected and the rate of acceleration being applied. It won't upshift until it has determined that the vehicle will maintain its speed and rate of acceleration chosen by the drivers input after it would make the shift. If it determines it can't do that, it keeps the transmission in the same gear. Assuming of course that you have an Allison.

[D-max Man]

When you engage the tow/haul mode, you will cause the transmission to raise the line pressure (To keep clutches securely applied) delay shift points (to prevent "shift business" as described by SoTxPollock) and it keeps the torque converter locked up all the way down to second gear on deceleration (to aid in breaking). Normally the converter only locks in 4th & 5th gears.