Justhereforinfo

iTrader: (2)

Ever since my engine swap, (4.8->5.7) I've noticed upon deceleration the transmission downshifts a bit late. It feels as if the engine RPMS drop lower than usual waiting on the trans to shift, almost stalling the engine.

During the engine swap, the trans slipped off the jack stands. The rear trans mount saved it from hitting the floor, and didn't appear to cause any damage. I replaced the mount and inspected the fluid lines and wiring, but found no damage.

Is this slow/late downshift conducive of an underlying issue?

No other problems with the trans. Fluid is bright pink and clean, and it upshifts great.

This is the stock trans in my 2003 silverado.

Thanks

mrvedit

All shifts are determined by the PCM.
The only way to tell if the trans is acting up is to use a scanner that can log the shift commands to verify that the trans is immediately responding to them.

I suspect the problem is in the tune. Was the PCM retuned or replaced during the engine swap?

Justhereforinfo

iTrader: (2)

Yes, the truck was tuned by a very reputable certified tuner. I'd like to give him the benefit of the doubt, but I can't find anything mechanically wrong with the trans. I also have a small idling issue, where the rpms fall too low during low speed turns.

If I wanted to pull the tune file and have someone else take a look at it, what software/hardware would I need to purchase? It was tuned with EFI live and I know the file is unlocked.

Is there one software that can edit tunes and perform the scans you mentioned?

mrvedit

I only know of EFI Live and HP Tuners; both can scan with logging, edit tunes, etc.
I suspect that 70% here use HP Tuners. Expensive at $650, but that is what it is.

A simple scanner that you can borrow free from many chain auto stores might still be useful. It would let you check that the TPS and MAP sensors are working properly.
I assume the speedometer is reading the correct values.
Some general-purpose scanner will show the commanded gear position, some do not.