2005 silverado 1500 4.10 gears and 33 inch tires. I have a 6.0 lq4 engine and a rebuilt transmission with a higher stall converter. Transmission went out so I told my transmission guy to put a little bit higher stall in it because I eventually want to do a cam. it is about a 2400 or a 2600 stall converter. My truck does not stay locked up on the highway. It only is locked up while increasing speed on highway and going up hill. Once I start going down the hill it unlocks and won't lock back up. I just changed my gears from 3.42 but it didn't even lock up before either. Any ideas. It seems like went that transmission is not warm it will lock up on back roads but once I get to the highway and at higher speeds it won't lock up. Talked to my tuning guy and he said it shouldn't have anything to do with his tune.

 

So it wasn't retuned after the new higher stall?

If not, I'd start there first.

 

Yes I did. I went back after my transmission rebuild and got him to adjust my shifts and I did tell him that I got a new torque converter. I just went back to him yesterday and told him about it not locking up and got him to adjust for my new gear set up

 

Do you have lock up now?

 

It will lock up fine when my transmission is cold. But once I get to the highway it will come unlocked with a random misfire code. I think it’s at higher speeds. The emission light will flash then go away and it won’t show a code. But I think that’s causing the tourqe converter to not lock up. And I can’t figue out what is making that light flash.

 

Log misfires, figure out the cylinders and diag the problem from there.

Past that if you never swapped misfire diagnostic information within the tune for the switch from the 5,3 to 6.0, that will need to be done. The misfire diag is different between the two engines. You can also raise the tables within the tune if you are positive you are not having real misfires.

 

I just got my 80 shifting right after my swap. Didn’t have Lock up either and second shifted a bit shard and late.. I was scratching my head because I tried the tables, this that and everything else I could think of and/or read then seen your issue so I chimed in looking for answers.. anywho. My VSS caliberations were not kosher with my ecm. I’ve tripled checked my numbers & caulcations and all were where they should be. Long story short I essentially had to cut all my numbers in half. Speedo works and trans shifts like a dream and I have LOCK UP�� All because my ECM didn’t like my numbers. Doesn’t make sense unless some 80e’s have different VSS rings in the trans then some others and or same with some NP246 t cases.. in an attempt to shorten this up again it was all VSS related and something in the tune, ECU or tccm doesn’t like a few numbers. From all I can gather all 80’s and NP246’s have a ring for 40 VSS pulses pr revolution so it’s got to be something wacky that’s beyond what can be addressed. Tricked the ECU with some bogus numbers and I’m bangin all 4 as should.. doubtful this was any help but there’s always a small chance. Good luck man