Have some questions about LLY and the role defuel plays in the trans shift feel. The truck is an 05 LLY with a built trans and has efi-live, other than that it’s stock mechanically.
I really like how truck shifts with the factory tune with low throttle input but with the dsp5 tunes, the shifts seem to hang a little unless I’m over 30-40% throttle which makes driving around town annoying. Is it the defuel in the dsp5 tune that makes the shifts hang or something else?
When the transmission is going to schedule a shift, it will send a request to the engine to pull a certain amount of fuel right when it's dis/engaging the clutches. This is necessary to prevent excessive wear and tear and also potential tie ups
Shift quality is all in how much fuel is being delivered vs how much the transmission expects to be delivered that make for a smooth shift. There is a fine line between too little fuel and the transmission causing a blip in power along with a quick shift that can be harsh. And too much fuel that makes the transmission hang and then bang into gear. Both are undesirable
A quality tune will balance the difference and mke a smooth shifting trans with good power too.
Some thoughts about DSP tunes. The Allison transmission has a learning algorithm that tries it's best within it's limits to account for variations in fueling, clutch wear, engine power, speed, RPM, and possibly a dozen other variables. When you switch tunes it makes a big change to these variables and the transmission has to learn the clutch on coming and off going pressure and speed all over again to smooth out the shift. This is going to create a harsi shift until it's done learning
And, DSP tunes only have a single table for defuel that is used for all 5 tunes. This makes it so you can't make a perfect shifting tune for the remaining other four. Good tuners can sometimes make a good compromise or have some tricks in the tunes they can do to help, but it's never going to be as good as a single tune.
If you are doing the tuning yourself, you are welcome to use the defuel calculator I make that is in the calculator sticky under the forum suggestions
If you have a tuner then they are going to need to fix it
There is also the possibility of mechanical issues like a plugged up fuel filter or bad injectors, sensors, etc that can make the power or fuel delivery different then expected and do similar things. Stock tuning can sometimes help with determining which one it is
