4l60e shifting issues fixed with restart. What gives?

[Norcalsparky]

Hey all,

I've got a 2001 Suburban 1500 LT 4x4 and it's been the best vehicle I have ever owned. However, it recently started having a shifting issue when it comes to shifting into 2nd & 3rd gear. The trans definitely isn't slipping it's just at totally random times it won't up shift.
I replaced both shift solenoids and discovered that one was practically falling out I thought that was surely the issue, but the problem is still there. When it's not acting up, I can get on it and the trans responds and shifts perfectly fine, but once or twice a day it will not upshift for no apparent reason. However, when it acts up, I pull over and turn the truck completely off and then restart it then its fine for the rest of the day. It seems to be something electrical since restarting seems to reset something and restore proper shifting.
Anyone heard of this before or have any ideas of where to look for the issue? I do a lot of work on cars but this has got me stumped.
Thanks

 

[mrrsm]

What about the General Condition of the Transmission Solenoid Harness. Is it too involved to replace that as well if it has Continuity Issues?

 

[Norcalsparky]

What about the General Condition of the Transmission Solenoid Harness. Is it too involved to replace that as well if it has Continuity Issues?

The harness looked good visually, it would not be too difficult to replace. Probably worth a try.

 

[Mooseman]

When was the last fluid and filter replacement? Condition of fluid? There have been instances of bad shifting caused by a plugged filter.

 

[Norcalsparky]

When was the last fluid and filter replacement? Condition of fluid? There have been instances of bad shifting caused by a plugged filter.

I replaced the trans filter and fluid when I replaced the shift solenoids.

 

[Mooseman]

What was the fluid like? Any metal in the pan? What's the mileage? Maybe one of the accumulators is damaged. When it acts up, have you tried shifting it manually?

It might not be necessarily an electrical issue. Maybe when the engine is shut off, the removal of internal pressure might be what's resetting it, hence why I think it might be a damaged accumulator, which are made of plastic.

 

[Norcalsparky]

What was the fluid like? Any metal in the pan? What's the mileage? Maybe one of the accumulators is damaged. When it acts up, have you tried shifting it manually?

It might not be necessarily an electrical issue. Maybe when the engine is shut off, the removal of internal pressure might be what's resetting it, hence why I think it might be a damaged accumulator, which are made of plastic.

The old fluid was fairly clean and I didn't see any shaving in the pan. The truck sits at about 195k, although the trans was replaced at around 120k. Manually shifting normally doesn't help, but pulling over and restarting does the trick. Every once and awhile the manual shifting corrects it, but rarely.