Shifting problem

[Michael Welch]

I have a 2004 Chevrolet Silverado 2500 HD. The problem start with the shift from 2nd to 3rd. When you get on it hard it will not shift untill you let of the throttle. Shifts fine while driving normal. Now when you are doing like 55 and you step on it it will down shift and only do about 2300rpm and go and faster untill you let off the throttle and let it shift up. Any idea what is wrong?

 

[THEFERMANATOR]

When did you last change your fuel filter? Shifting problems is one of the 1st signs of a plugging fuel filter.

 

[Matthew Thieme]

When did you last change your fuel filter? Shifting problems is one of the 1st signs of a plugging fuel filter.

If slow flow from a filter can cause it, could a sluggish lift pump have the same effect?

 

[btfarm]

Along with the possible fuel filter issue, when was the last time the Allison spin on filter was changed?

 

[MrMarty51]

If the TOW MODE is engaged, would that affect its shifting ?

 

[THEFERMANATOR]

If the TOW MODE is engaged, would that affect its shifting ?

Tow haul mode raises the part throttle shift points and locks the converter in 2nd gear. Otherwise they aren't that different. A plugged fuel filter, boost problems(boost leak), and dirty MAF are the normal culprits. A plugged spin on can cause slippage since you'll lose pressure to the valve body.