4l60e 3rd gear gremlins
 

So I just finished a 5.3l/4l60e swap in my 67 C10. It has gone great until now when I got ready to test drive. As a note, i had no history on the trans other than it had a rebuild date of 2007 on the bellhousing. So I accidentally broke the teeth in the oil pump for the trans when installing so I had to replace that. Once that was replaced and tested, I had issues with 3rd gear. It didn't want to shift into 3rd and acted as though it was slipping or going into "neutral". After many tests and help from a friend that works on transmissions we have done/replaced the following.

1-2 and 3-4 Shift solenoids, 3-2 downshift solenoid, TCC solenoid, force motor, pressure switch, Transgo shift kit, drum, rebuild kit, bonded pistons, rotor kit, 1800-2000 stall converter, release springs, 3-4 ball and capsule.

I am am still having issues with 3rd gear. Sometimes it will shift into 3rd fine(not usually), sometimes it will go into 3rd and then jump around back and forth to 2nd or 4th like it's hunting. Other times it will act like it's slipping and go into "Neutral". We tested with another PCM to make sure it's not the tune.

Also, if you use a scanner and tell it to shift, it will shift fine every time. It only acts up when it tries to shift on its own. When you watch the 1-2 and 3-4 solenoids on the scanner, they are going crazy when it is trying to shift into 3rd. They have been tested and replaced though.

Right now we are thinking it's a pressure issue somewhere in the Valve Body...

any and all advice would be great. Glad to finally be a part of this forum. I've heard a lot of good things about the people on here

Is the tune stock or modified?

basic stock tune for LS swap. Just disable VATS etc. I tried two PCMs from two different LS swap tuners and had the same results from both.

If the solenoids are freaking out I would suspect a wiring issue. Most likely a ground.

That would make sense. Would it shift normal with the scanner though if it had a bad ground? I have not road-tested with the scanner yet, but on the lift, it shifted perfectly when we controlled the shifts with a scanner.

I would suspect VSS issue here is why obviously if your seeing the solenoids switched off and on with the scanner automatically and yet can force 3rd electronically its not a solenoid issue its a commend issue. Wiring would be unlikely as it would still affect the forced shift also open and shorts should set codes with the PCM.
It certainly does not sound like a trans mechanical issue of any kind,
Like I said look at VSS and TPS signals carefully, Also if used check that MAF signal and tach signal are stable not jumping around.

thanks for the advice. I am running a MAF and I have replaced the VSS and TPS sensors when I first installed the motor just for the sake of having new parts. I will double check them all though with the scanner to make sure they are reading correctly. The only issue with the codes is that I haven't driven it enough to really trip a code and I've unhooked the battery a lot in between which would reset it.

I don't have gauges yet so I hooked up my Bluetooth OBDII port and checked my gauges on my phone. After a quick drive through the neighborhood I quickly noticed that my Speedo was growing crazy the whole time. I really hope this is my issue with the 2-3 and 3-4 shifts. I'm going to put in a new VSS and see what happens. If that doesn't work then maybe a have a short from the VSS to the PCM? It does seem that something with the VSS signal is causing my problems.