Let me preface this by saying I am only looking for help on my transmission. Thanks

I bought my 2005 Silverado 2500hd a year and a half ago with 279k miles. It has a 6.0 gen3 with a 4l80e and 4.10s. I didn't know what I was buying and am too far deep into the hole now so might as well build it good.

My transmission lost reverse at 285k the previous owner said it was rebuilt at some point. I bought a used 4l80e for $500 said it had 160k swapped it in 500 miles after I lost reverse and that trans didn't have reverse either so I gave both to a guy who said he could fix reverse on my original and I sold him the other one for $300. He fixed reverse on my original trans for $100. That was fine until I started pushing the truck. 1st and 4th slipepd under heavy load and it was hard and soft shifting. 1st would fall out with 1000lbs in the bed on a freeway onramp over 4k rpm. 4th would fall out at like 100mph and has fallen to like 95mph as of recent. It would hard and soft shift seemingly randomly I could not get it to hard or soft shift twice under similar conditions. Reverse is now solid as a rock I accidently shifted into reverse going 45mpg and it locked and spin them backwards without missing a beat.

I was fine with this until recent 1st and 4th have been getting worse so I grabbed another 4l80e from LKQ out of a 2000 suburban and was planning on swapping it in a few weeks but the last two days I hauled a 2000lb trailer about 250 miles in stop/go conditions. The trans was working fine during this endeavor. I drove it yesterday evening and it was working fine. I started it up this evening and the 1-2 shifts were slipping pretty bad this progressed into the trans not shifting at anything over 2.5k rpm. Trans temp was 45 degrees over what they usually are, I do have a trans cooler. Every shift is delayed 3-4 secs and it is shifting hard 95% of the time.

It has become more or less undriveable so I am planning on swapping my transmission with the other used transmission from LKQ tomorrow. Hopefully that one works alright and I have a working truck again because I have to swap the motor in 2 weeks.

So given all that information I am looking at either selling or rebuilding my old trans so when the LKQ trans fails I will have something reliable. My old trans has had at least 3 different people inside of it and is at least 290k miles.

I am looking for advice as to what anyone might think the trans issues are and if it realistic that I might rebuild it. I am fairly mechanically inclined and have rebuilt an engine but have never done a trans but I have successfully swapped 2 of them. Is it worth me trying to fix or just having a trans shop do it a local shop quoted $1300 for a stock rebuild with a year or so warranty. Any input is greatly appreciated. Thanks

 

The 4L80E is a great, strong, and long lasting Transmission when they are maintained.

You have had some old, tired, and probably severely lacking TLC Transmissions... I feel that is more than likely, simply the issue.

I would go for the $1,300 rebuilt Transmission, a new Torque-Converter, and a Flushed-Out Transmission Cooling System.
I consider that amount of money inexpensive compared to constantly swapping Junk-Transmissions.
It just seems like a waste of time and money to keep repeating the same process that you have been following.

A Transmission re-builder who is familiar with the 4L80E (updates/ hydraulics for Direct) should be able to have a Transmission for you STOCK...
That will handle 500 to 600 Ft/ Lbs of Torque in a Full-Size Gasoline Pick-Up Truck, for a few Hundred thousand miles.

 

DIY'ing an 80e can absolutely be done, but you will need an abundance of patience, tenacity and attention to detail.