If you never tuned your transmission, eventually the 4L60E will give out. Id recommend driving it until it dies then do a transmission swap. Lucky 4L60E are so common you could find one for cheap. Its worth dumping the money into your canyon and make sure to get it tuned. Im at 202k miles or 326500km and mine still shifts great. Id be more worried if youre going to 4500-5000rpm on flat ground and it still doesnt shift.

 

Unfortunately, you are likely in need of a swap or rebuilt. They are plentiful, so used ones are easy to find. And ever trans shop tech has rebuilt dozens of them too. You have to make sure a used one is compatible with your trucks electronics, but I am not very knowledgeable on how to decipher that.

 

do you think theres another explanation? i dont understand why it would work perfectly now. today it stopped working in reverse, but that lasted until i put it in park then back to reverse

 

Just 1 possibility,modern transmissions are complex.When you drive a failing tranny you usually tear them up worse.

Symptoms with possible repairs:

1. Slow, slipping or no reverse: “lo-reverse” clutches are worn out, fluid leak in the reverse apply circuit, or broken sunshell. It is possible to remedy a fluid problem by removing the checkball from its cage in the case in the rear of the trans may help (must remove valve body), or adding a high-viscosity additive such as Lucas Transmission additive or other seal restorer product. May also have worn boost valve (can replace in the pan).