4l80e Question

I have a 2000 Chevy K 2500 with the 4l80e (167,000miles). For about a year the trans will shift out of overdrive randomly while driving. When this happens, 1st to 2nd and 2nd to 3rd shifts hard. The trans stays this way until I stop, shut off the key for a few seconds and restart it. After restarting the truck it shifts fine again for anywhere between 5 to 100 miles then it shifts out of OD again. It never has set any codes for the trans. Changed filter & fluid (not burnt). Had no effect. Any help would be appreciated, Thanks

Try running a ground wire from clean shiny metal on the transmission to clean, shiny metal on the engine block or frame. The reason is that electrolysis can occur between the aluminum transmission, the cast iron block and the steel bolts that hold them together which won't affect the structural integraty, but can affect the electrical ground the transmission's computer needs.

I hate to tell you this but it is time for a new trans. What happens is there are two speed sensors in the trans, the input sensor and the second is output speed...The computer uses the two sensors to figure out how fast the truck is going and which gear the truck is in. When the trans slips it confuses the computer and it defaults into 3rd gear loosing 4th. It probably will drive fine for a while then one time you will try to up a steep hill and you will notice higher then normal rpms. My suburban did the exact same thing and the dealer just kept replacing the speed sensors. Then on a very steep hill I realized what was going on. You can run it by a local trans shop but I bet they will say the same. Like I said in my case it still drove fine just slipped under load and under load it would drop

good luck, mark

i have a 92 2500 with the same trans and it was the high pressure solenoid was bad a few other ones in the trans take it and have a trany place put computer tool onit cuz it saved me from haveing to by a new trany or have it rebuilt but good luck