4l80e acting funky

[Lookin4the1]

I've got a 6.0 with a 4l80e. I've put about 600 miles on it since the swap and it wants to shift at odd points or too soon into overdrive or 4th. it will also downshift itself out of no where. when i start out in OD. I've just been manual shifting and going through the gears and usually leaving it in 3rd unless i'm 60MPH. do i have a bad VSS sensor?

I'm trying to get it tuned next week, but theres no point if the trans is acting all crazy.

[BR3W CITY]

Originally Posted by Lookin4the1

I'm trying to get it tuned next week, but theres no point if the trans is acting all crazy.

Not true. If the issue is happening because of a tire size problem, or lockup/shift settings that don't gel with your rear end and tire size, then you can get all sorts of shifting issues.

Are you getting any codes indicating a mechanical failure?

[Lookin4the1]

no codes thrown at all.

[ls1nova71]

Originally Posted by BR3W CITY

If the issue is happening because of a tire size problem, or lockup/shift settings that don't gel with your rear end and tire size, then you can get all sorts of shifting issues.

This. It sounds exactly like you don't have the correct rear gear and/or tire size. Get a tune and let us know how it is.

[Lookin4the1]

The best money I've spent on this swap so far. I never would have thought that a simple street tune would turn this truck around. The tuner said every setting on the trans was absolutely wrong and whoever tried to tune it before was an idiot. The trans actually shifts soft and smooth and when I accelerate it acts right.

[mongocanfly]

glad to hear your shifting now..did you also get your engine dyno tuned as well? ...that'll also be money well spent

[Lookin4the1]

They just took it down the road for about an hour and played with it for drivability. I will probably put it on a dyne down the road.