Problem with lock up on a 91 4L80

[draginlow]

Need some input on a problem I'm having. Little back ground on this. Back before the rebuild on this truck I had a problem with the trans slipping and lock up kicking in and out. At first we went after the electrical side. It had a chip in the ecm when I got it. At times it wouldn't start and found the chip in the ecm was lose. So I removed the chip and replaced the ecm. Truck started fine after that but the trans still acted up. I pulled the pan to find a crap load of Metal shavings. We I did a full rebuild. The trans was full rebuilt and all upgrades were done to help with towing. New trans cooler and lines along with all new gm solenoids.The truck side harness was cleaned up and all re wrapped. It has a new brake switch and tps. Now it's back on the road I'm still having the lock up problem. It doesn't happen any particular time. I've held up and the brake peddle and it will do it even coasting downhill off the throttle. It doesn't do it all the time. I drove it for 2 days with no problems then next day it was doing a constant. It will just keep kicking out and go right back in. Anyone and any suggestions on what to try to pinpoint this problem? Or what wire I can put power/gnd to just lock this up off a toggle? I just want to drive this truck without messing up my new trans. Thanks for any input and sorry for the long read ha ha. Here's the truck.

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[Oldblue98]

My 1998 5.7 had the same problem, always back & fourth in TCC . It would send a code of slipping.
Now my truck had a Hypertech programmer for years. And this had been a consistant problem with the lock out in and out in and out up around 60 mph . I had 2400.00 worth of rebuild done to end up with the very exact same problem. Took back to trans shop three times, still same. So me being one to solve problems, I went on a mission of learning.
The Hypertech programmer to work right it required a 160 degree thermostat, well when I started checking it was not warming up enough for the PCM to let it lock out like it should. I shot it with a infrared at the thermostat at full operating temp and it was only getting to 155-156 degree. The things I read said temp should reach at least 157 - 160 . So my idea was it was not getting quiet hot enough and it was bouncing in and out.
So I put the programming back to stock settings , stock shift points and installed a 195 thermostat back in it. Problem solved !!!! 2400.00 bucks later
I am not saying this is your problem, but it was as simple as that for me ! I had trans rebuilt and new Converter put in . Only thing that boils me is the transmission shop did not or could not figure that out by process of troubleshooting ! Once I made my mind up to do it myself, it took a GM service manual, a Scanner, a infrared gun to shoot temps at various locations such as radiator, thermo housing, heads !

 

[Big D]

my 91 was kicking in and out of lock up as well on the freeway, Like I had to keep it at a certain speed so it would calm down.

first the check engine light came on and the truck would rev up super high and then slam into 2nd gear, checked engine codes.... tps, got a "New" Tps ... check engine light goes away, I give the truck to the old lady to drive, she says its much better.... a few weeks later I drive it on the freeway and noticed its kicking in and out of lockup.. so I start doing research, everything is pointing to either solenoids or the torque converter, So I buy the upgraded solenoids and a torque converter (wish I didnt) while parts are en-route I find an article showing a bad TPS without a check engine light.... so I took my "new" TPS back to autozone, claimed it was faulty, they gave me another TPS......Fixed!

In my experience the after market OEM parts for this particular truck suck a dirty set of nuts... Id try another TPS, its cheap and easy.... I know yours is new, but I just got done with a head scratcher of a no start condition, and I automatically didnt check the distributor because it was new, and stupid me, why would I ever consider a new part to be fully functional.... (blatant sarcasm)

 

[draginlow]

I broke down and took it to the dealer. Ended up being a spread terminal at the ecm for the 5volt reff to the throttle position sensor. She is shifting like a champ now. It had a new sensor and a new distributor also. I used a gm tpms sensor and had a good quality distributor already. Those were the first things to get changed lol.


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